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1. Hash File Overflow Area 1 Overflow Area 2 Position in the Hash Key Position in the Hash Kay Position in the Hash Key hash table overflow area 1 overflow area 2 Position 0 000 Position 1 001 Position 114 114 Position 114 114 Position 115 115 Position 243 243 Position 243 243 Position 243 243 Position 348 348 Position 349 349 Position 349 3497 Position 349 349 Position 452 452 Position 665 665 Position 666 666 Position 666 6667 Position 666 7 666 Position 667 667 Position 999 999 3421999 999 Methods of access performed on different file organizations When performing serial access primary key of the search record is compared with the primary keys of the records in the file When performing direct access primary key is converted to a pointer and the processor jumps directly to the memory location of the record in the file pointed by that pointer to access the record Www revision notes co cc Serial Files Sequential Files Indexed Random Direct Sequential Files Access Files Serial Access Performed Performed Performed Not Performed Direct Access Impossible Impossible Performed using Performed using pointers called pointers called indexes hash keys Page 46 of 115 20 What are the criteria to go by when deciding which file organization is suitable for a giv
2. 6 The processor sends another block of data to fill the buffer Peripheral devices Hardware that is connected to the system unit from outside are called peripheral devices Examples of peripheral devices are Input devices such as keyboard mouse digital camera microphone Output devices such as monitor printer speaker Page 53 of 115 wWww revision notes co cc z6 Storage devices such as external hard drive and flash drive Communication devices such as external modem and ADSL adaptor What are input devices This is a piece of hardware that allows data to be input to the processor What are output devices This is a piece of hardware that allows the processor to convey the results of processing information What are communication devices This is a piece of hardware involved in transferring data between computers Examples are modem network interface card router bridge and ISDN adapter The details will be covered in Chapter 6 Input Devices 1 Keyboard The common keyboard which contains all the ASCII keys is called the QWERTY keyboard because those are the first six characters on the top line The keyboards of special devices do not contain all the keys of the common keyboard but only the keys that are needed for the operation of that device Examples are ATM machine washing machine door security systems etc ATM machine needs only those keys for numbers to enter an amount of money and for Enter and
3. 2 The software can be written to run on specific hardware 3 The software can be integrated with existing software 4 There may not be a suitable software package required for the purpose available in the market Disadvantages of custom written bespoke or tailor made software packages 1 Needs to hire a software engineer with that specific developing skill and experience 2 Expensive to develop What is an Off the Shelf Software Package This is a software package that has already been developed and is immediately available to buy 2 It is a software package which can be used to carry out all the common tasks related to a specific business area 3 Examples for off the shelf software packages are Income tax processing system Airline reservation system Hotel reservation system Advantages of buying an off the shelf software package 1 Software is immediately available 2 Low price compared to have it developed by a specialist 3 Since the software has already been tested and used for sometime by so many variety of users it is assured that any bugs should have been found and rectified 4 Includes all the common features of the system concerned as the developer who has done the system analysis has expertise in that field 5 New releases or editions will be available 6 Because the software is in general use by many users well established training courses are usually available Page 8 of 115 Www revision not
4. Page 97 of 115 Www revision notes co cc Chapter 1 9 Handling of Data in Information Systems What is manual data collection Manual data collection involves the following three stages 1 Collecting data 2 Preparation of data suitable for computer use 2 Inputting data to the system What is automatic data collection Automatic data collection involves the following two stages 1 Collecting data 2 Inputting data to the system Methods and devices used for automatic data collection 1 Barcode reader 2 OMR 3 OCR 4 MICR 5 Voice recognition 6 Magnetic stripe card 7 Smart card 8 Data logging 9 Touch screen 10 Digital camera Methods and devices used for manual data collection 1 Keyboard 2 Mouse Examples of situations where manual data collection is used 1 Obtaining data from data capture forms 2 Obtaining data contained in turnaround documents What is data verification This is the method of checking whether the data entered to the computer is same as the source data www revision notes co cc Page 98 of 115 In the case where the data are contained in a source document the verification can be performed by using the following two techniques 1 Proof reading method Here the operator manually checks each and every piece of data entered to the computer against the corresponding piece of data in the source document to see whether they are same 2 Double entry method Here two
5. 2 Why evaluating the new solution against the initial specifications is important to the end user System documentation System documentation explains 1 How to use the system 2 How the system has been developed and 3 How to maintain the system System documentation is done at several stages of the system development life cycle Following are the different types of system documentations 1 System requirement specification This documentation contains the list of the requirements that the customer needs to have in the the new system which have been described under the system requirement specification section Page 91 of 115 Www revision notes co cc 11 a List of tasks to be performed b Specifications of data c Input specifications d Output specifications e Structure diagrams System design specification This documentation describes how the system would be developed This includes a Specifications of the hardware specifications of input devices output devices data storages computers and other equipment b Specifications of the software used whether it needs a database management system a programming language tool a user interface design tool etc c Design of the data files and databases d Development methodologies used e Testing strategy Program specifications This documentation describes the method of developing the program a Detailed algorithms used represented by
6. 6 Even though the hash keys are stored in the sequential order in the hash table the records in the random access file may not be in the sequential order How a program access records in a random access file 1 The program which searches a record in a random access file calculates the hash key of the record being searched by applying the hash function on the record s primary key which is entered to the program by the user 2 The computer program then accesses the absolute memory or disk address pointed to by the hash key This is the location where the search record is stored 3 If the same hash key occurs more than once in the hash table this happens if there had been collisions while writing the hash keys to the hash table the computer program which searches the record accesses the primary key pointed to by each occurrence of that hash key to find the matching one 4 A computer program can access records in a random access file only directly but not sequentially What is a hash function or hashing algorithm Hashing algorithm is a formula that is applied on the primary key of a record to calculate the address of the relative memory location where that record should be saved An example is h key key MOD 1000 Where key is the primary key h key is the hash key 1000 is the number of records intend to be written on the file key MOD 1000 gives you the remainder after dividing key by 1000 Example 2543876
7. 65535 What is a field This is the storage space for one data item What is a record This is the data structure which contains all the data about an instance of an entity What is a fixed length record This is a record where each field is defined with a specific length What is a variable length record This is a record where at least one of its fields has a varying length What is a file This is the data structure which contains the data of all the instances of an entity Page 29 of 115 WwwW revision notes co cc Estimating the size of a file When the fields of the records containing in the file and the approximate maximum number of records in the file are given the size of the file can be estimated Some acceptable field sizes according to the Cambridge International Exam mark schemes are given in the following example A file contains records which has the following fields Customer Name Telephone Number Item ID Item Name Price Order Date Whether or not the Order Outstanding Whether or not the Order is paid for It is assumed that there will never be more than 10 000 records in the file Estimate the size of the file Field Name Minimum Length Maximum Length Customer Name 10 bytes 30 bytes Telephone Number 5 bytes 20 bytes Item ID 2 bytes 4 bytes Item Name 10 bytes 30 bytes Price 2 bytes 4 bytes Order Date 2 bytes 8 bytes Whether or not the Order 1
8. Digitizer This is an input device which can convert text a picture or a drawing which are considered as analog signals to digital form when trace over them 19 Smart card Used as telephone cards to input the card number and the amount of the card Used as credit cards to input the account number and the credit limit 20 Magnetic stripe reader Used to input the data containing in the magnetic stripe of a credit card 21 Touch tone telephone Used to input responses to a voice based menu system by pressing keys of the telephone 22 Kimball tag This is a piece of card with holes punched in it which represents a code When an item is purchased the card is removed and input to a computer Used in clothes shop for stock control What is point of sale POS Point of sale is a terminal connected to a main computer The input devices used at a point of sale are 1 Barcode reader scans the barcode fixed to an item by recognizing the thickness of the bars to allow the interpretation of the item number 2 Keyboard allows the operator to input barcode price and other details manually in case the barcode reader cannot read the barcode 3 Swipe card reader or the smart card reader Allows reading data from a credit debit bank card or to send those details to the bank 4 Scales To measure the weight of an item 5 Customer keypad For the customer to input the PIN Page 58 of 115 WwwW revision notes co cc ll T
9. Ring Topology In a ring network the two ends of the bus are joined up This creates a loop so that data can be sent in both directions along the cable If there is a break in the cable the network will continue to operate because the data can go in the other direction Workstation 3 Workstation 1 Workstation 5 Workstation 2 Workstation 4 Workstation 7 Workstation 6 Advantages of ring topology gt There is no dependence on a central computer or file server and each node controls transmission to and from itself gt Can continue with a break in the network cable as the data can move in both directions along the cable gt High data transmission rates are possible Disadvantages of ring topology gt Ifone node of the ring breaks down transmission between any of the devices in the ring is disrupted Types of data transmission Data transmission can be divided into the following two types gt Serial transmission gt Parallel transmission Page 75 of 115 Www revision notes co cc Serial transmission is the transmission of data one bit behind another along a single wire eoe o o o o o o _e Parallel transmission is the transmission of data along a set of several wires usually a multiple of eight wires where bits move simultaneously as a bit front Parallel transmission is faster than serial transmission Parallel transmission is less reliable than serial transmission because of the fine t
10. STOP ENDIF Page 36 of 115 WwwW revision notes co cc m RN Algorithm 5 Deletion of an item from a stack when the stack is represented by an array j Memory addresses increase in this direction Stack Pointer points to the top of the stack IF stack is empty DISPLAY message Stack is empty STOP ELSE READ the item to be deleted Set data in the cell pointed to by the stack pointer to the variable item_deleted Decrement the stack pointer by 1 STOP ENDIF Algorithm 6 Insertion of an item to a queue when the queue is represented by an array If the Head pointer points to the front of the queue and the tail pointer points to the back of the queue f Memory addresses increase in this direction Tail Pointer points to the back of the queue Head Pointer points to the front of the queue IF queue is full DISPLAY message Queue is full STOP ELSE Page 37 of 115 Www revision notes co cc ll Increment tail pointer by 1 Store the new data at the location pointed to by the tail pointer STOP ENDIF Algorithm 7 Deletion of an item from a queue when the queue is represented by an array If the Head pointer points to the front of the queue and the tail pointer points to the back of the queue j Memory addresses increase in this direction Tail Pointer points to the back of the queue Head Pointer points to the front of the queue IF queue is empty DISPLAY message Qu
11. Www revision notes co cc LAN is usually hard wired uses cables to WAN requires other transmission media to connect computers connect devices except for cables Data in a LAN is easier to keep secured Data in a WAN is prone to hacking Computers in a LAN can share hardware such Computers in a WAN cannot share hardware as printers such as printers What are the software and hardware needed for communication in a LAN l Network operating system Needed by the computers to get connected to each other and communicate data and information Hardware drivers for the network interface card and the modem Needed by the network interface card to convert data and information to a format that the processor of the communicating computer can understand Network interface card Need by the computers to get connected to each other Cables Used as the transmission medium Hub Used to concentrate the cables connected to the computers What are the software and hardware needed for communication in a WAN 1 Dial up software To connect to a Web server or to access the telephone lines 2 Network interface card 3 To communicate ina WAN Modem ISDN ADSL adapter To access the telephone system What are the advantages of using a network of computers over using a collection of stand alone computers It allows the sharing of hardware resources such as disk storage printers image scanners modems and central serv
12. from An example for an interactive information system is an exam marks processing system from which the user teacher can obtain information by producing reports and can alter the data by changing or entering marks to the system What is management information system MIS This is an information system that a manger of a company can access to obtain information about the performance of the business What are the two types of management information systems 1 Condition driven or operational management information systems and 2 Strategic management information system What is condition driven management This is performing the day to day management functions Examples Ensuring that the business has enough stock Ensuring that enough employees are available to operate a production line What is strategic management Page 106 of 115 Www revision notes co cc 2 RN This is the performing of management functions which involves making decisions which are long term in nature and are related to the policies and objectives of the company What is condition driven management information This is information such as decisions reports and responses produced as a result of meeting some parameter Examples The stock level has fallen below the reorder level Sending a secretary working at the HR department to the reception counter of the company because one of the two receptionists is absent on that day What is strategic
13. Cancel commands Washing machine needs keys only to execute a specific set of commands such as Start Stop Hot Water Cold Water etc Door security systems need only the keys to enter numbers from 0 to 9 which are used enter the password Problems with normal keyboard are 1 Prone to damage from dust dirt and liquid because of the gaps between the keys 2 Difficulty to keep the typist s hands comfortably while using the keyboard because the keys are arranged in rigid rows Page 54 of 115 WwwW revision notes co cc Concept keyboard This is a keyboard which has specialized overlays to perform functions with specialist software After the keyboard is programmed a sheet called an overlay is placed overtop to identify each key The overlay can consist of any combination of words symbols or pictures Usually this keyboard has its keys simply as areas of a continuous surface which are sensitive to touch They are ideal for outdoor use because the rainwater will not damage them Example The keyboard of an ATM machine Ergonomic keyboard An ergonomic keyboard is a computer keyboard designed with ergonomic considerations to minimize muscle strain Some ergonomic keyboards are a single board with the keys separated into two or three groups allowing the user to type at a different angle than the typical straight keyboard Some ergonomic keyboards have the keyboard split into several independent pieces Either of
14. analyst to test how the system would perform with a smaller amount of data The disadvantage of this method is that it is not possible to check how the system would perform with a large amount of data which is the actual case when it is implemented at the organization level 3 Phased implementation The system is implemented by replacing the parts of the old system gradually with the corresponding parts of the new system while the rest of the system is still running with the old system Page 94 of 115 WwwW revision notes co cc 14 The advantages of this method are that a Can repair a faulty module without affecting the other modules d It allows staff to be trained gradually The disadvantage of this method is that one or many part s of the old system and the part that has been computerized may not be compatible It would also take relatively a long time to fully implement the new solution Examples of systems which are ideal for phased implementation are Example 1 Process control system of a chemical plant 1 One phase can be the computerization of the mixing of raw materials monitoring and controlling the conditions such as the temperature and pressure involved with one reaction 2 Another phase can be the computerization of the packing process of the final product Example 2 ATM machine system 1 One phase can be the development of the withdrawing process of money 2 Another phase can be the development of the de
15. and hardware Has to hire additional staff to maintain the computers What are the health and safety issues that a worker who work with computers can get by working and how can they be overcome 1 2 Stress Take regular breaks RSI Use ergonomic keyboards and take regular breaks Muscle or back strain Use well designed chairs keyboards and position correctly when work in the computer Eyestrain Use glasses anti glare screens and look away from the computers Poorly designed environment such as trailing wires Use a purpose built area and that the wires are properly concealed Extremely low frequency radiation Use of low radiation monitor limit time spent at terminal How can using the computers cause stress in an employee at his work place The fear he or she will not be able to learn the computer skills The fear that their position of seniority will be undermined by younger and junior employees with a high level of competence in ICT Impossibility of getting away from work since pagers mobile phones laptop computers and modems even after leaving the office there is no need to stop work Managers are bombarded with far more information than they can assimilate producing information anxiety What are the results of computer related stress at someone s workplace Failing personal relationships Loss of appetite Addiction to work Potential alcohol abuse What is Repetitive Str
16. byte 1 byte Outstanding Whether or not the Order is paid for 1 byte 1 byte Length of one record in bytes 33 98 Length of 10 000 records in bytes 33 10 000 98 10 000 Estimated file size in KB 330 000 1024 322 980 000 1024 957 Estimated file size in MB 333 000 1024 1024 980 000 1024 1024 0 315 0 935 Data Type of a field Numeric data type Numeric data type is assigned to data that are used in mathematical calculations There are different sub types of the numeric data type such as integer and real 1 Integer data type Integer data type is assigned to data that can be counted or the data that can be expressed as a whole number Examples are Number of students in a class Page 30 of 115 wWww revision notes co cc Number of cakes sold at the bakery today 2 Real data type This is assigned to data that may include decimal values Examples are Height of a student in centimeters Average mark of a student at the semester exam 3 Text or String data type Text or string data type is assigned to data which are not used in mathematical calculations These data may include any Keyboard character Examples are School admission number such as LW12345 An email address such as john smith_colombo yahoo com 4 Boolean data type Boolean data type is assigned to data that have values either Yes No or True False Examples are Is Male Is Married ASCII System ASCII
17. cannot access records in a sequential file directly What is an indexed sequential file 1 This is a file where records are organized in the ascending or descending order with respect to the primary key and where the records are divided into pages of equal size 2 The data pages of the index sequential file are associated with an index file Index is a pointer which contains the absolute memory or disk address of the first record of a data page 3 Index file contains two fields Primary key and the index All the records in one data page have the same index which is the memory address of the data page where that record is contained 4 Acomputer program can access records in an indexed sequential file both sequentially and directly How a program creates an index sequential file 1 The program writes the new record to the end of the file divides the records into equal sized pages and sorts the records within each page This process happens each time a new record is added to the indexed sequential file Page 39 of 115 WwwW revision notes co cc gt 13 2 Then the program creates the index file which contains the primary keys and the corresponding index of each primary key index is the pointer which contains the absolute memory or disk address of the first record of a data page 3 When the number of records containing in an indexed sequential file increases the number of pages in the file and therefore the number of i
18. files which should not be altered accidentally or purposely Rewritable CDs Rewritable CDs have all the properties of CD ROMs and in addition to that the data stored in the rewritable CD can be changed or erased Therefore rewritable CDs are used for storing backup copies of files and for archiving files Zip Drive This is a more robust version of a floppy disk Zip drive has a higher data storage capacity and a faster data access speed than a floppy disk Zip drive is usually used as a backup medium DVD This is an optical storage medium The data storage capacity and the access speed are much higher than the CD DVDs are used for storing large files such as music and movies Use of buffers and interrupts in the transfer of data from primary memory to the secondar storage It is necessary to transfer data between the primary memory and the secondary storage Because primary memory is part of the processor and that anything that goes in or out of the processor must go through the ALU This is shown by the following diagram Primary Memory Secondary Storage Primary memory operates at great speed because it is part of the processor In comparison secondary storage is slow at reading or writing data Buffer is an area of fast access storage which can be filled by the processor very fast and then emptied at a slower speed by the secondary storage device allowing the processor to continue with other tasks Therefore a buffer is in
19. operators enter the same set of data separately to the computer Then a computer program will be used to compare the corresponding pieces of data in each of the two sets of data files What is data validation This is the method of checking whether the data inputted to the system is reasonable and accurate There are several methods of data validations Length check Character type check Format check Range check Presence check Check digit When a piece of data consists of numbers one number is designated as the check digit The value of the check digit can be obtained by applying an algorithm to the rest of the numbers If the data is entered to the computer incorrectly or if the order of the numbers in the data were not correct the value calculated by applying the algorithm to the number will not be equal to the value of the check digit NnBWNre Methods of data entry used under given circumstances Situation Method of data entry 1 Entering data in the checks received at a bank MICR 2 Taking a photo to print on a sweatshirt Digital camera 3 Recording of an event taking place to display on Video camera the computer screen 4 Processing answers to an MCQ test OMR 5 Maintaining temperature inside a room using a Temperature sensor Thermostat 6 Burglar alarm Pressure sensor motion sensor light sensor 7 To pass pictures and video sequences between Using a digital camera and compressin
20. primary memory and the hard drive of the computer is half duplex 2 The data transmission between the computer and the printer is half duplex because the transmission of data files to the printer from the computer and the passing messages to the computer from the printer such as error messages happen at different times Circuit switching In circuit switching a fixed path through the network between the sending computer and the destination computer is opened and held for the entire time duration of data transmission Advantages of circuit switching The message arrives at the receiving computer without having its data to be reordered and reassembled Disadvantages of circuit switching Parts of the network are tied up for considerable periods of time Packet switching In packet switching the following things occur gt The message is split into a number of equal sized packets gt Each packet is labeled with the destination address and the packet number gt Packet switching transmits individual data packets into the network to find their way to the destination computer independently of each other gt At each node the label is checked and the packet is redirected gt At the destination computer the packets are reordered and reassembled according to their packet numbers Page 77 of 115 Www revision notes co cc Destination computer Sending computer Advantages of packet switching gt Large part of the net
21. sudden decisions about work 4 Incur costs in training programs 5 Group work becomes difficult What are the advantages to the society due to the workers working from home 1 Less traffic on the roads 2 Implies less need for infrastructure 3 Less pollution 4 Creates closely knit families 5 Can provide work for disabled What are the disadvantages to the society due to the workers working from home 1 Creates a society with less social ties 2 Non availability of trade unions which leads to dictatorship by the employers Why legislation is needed to protect the personal data of customers in a business Page 113 of 115 Www revision notes co cc l 2 de 4 3 6 Data may become incorrect Some information is confidential in nature Some data may be misused Customers may lose financially Customers may not be willing to provide data Business may lose potential customers What are the data protection principles mentioned in the Data Protection Act of 1998 l 2 Data must be fairly and lawfully obtained Data must be processed only for specified purposes Data obtained must be adequate relevant and not excessive Data obtained must be accurate and kept up to date Data must not be kept longer than necessary Data must be processed according to the data subject s rights Data must be kept securely against unauthorized access and accidental loss or damage Data must not be tran
22. system is used to represent the data generated by the computer keyboard ASCII Codes The ASCII codes of the keyboard characters are given in the following table Character ASCII Character ASCII Character ASCII Character ASCII Code Code Code Code NULL 0000000 Space 0100000 1000000 1100000 SOH 0000001 0100001 A 1000001 a 1100001 STX 0000010 i 0100010 B 1000010 b 1100010 ETX 0000011 0100011 C 1000011 c 1100011 EOT 0000100 0100100 D 1000100 d 1100100 ENQ 0000101 0100101 E 1000101 e 1100101 ACK 0000110 amp 0100110 F 1000110 f 1100110 BEL 0000111 s 0100111 G 1000111 g 1100111 BS 0001000 0101000 H 1001000 h 1101000 HT 0001001 0101001 1001001 i 1101001 LF 0001010 0101010 J 1001010 j 1101010 VT 0001011 0101011 K 1001011 k 1101011 SF 0001100 g 0101100 L 1001100 l 1101100 CR 0001101 0101101 M 1001101 m 1101101 www revision notes co cc Page 31 of 115 1 Nn 1 SO 0001110 0101110 N 1001110 n 1101110 SI 0001111 0101111 O 1001111 o 1101111 DLE 0010000 0 0110000 P 1010000 p 1110000 DC1 0010001 1 0110001 Q 1010001 q 1110001 DC2 0010010 2 0110010 R 1010010 r 1110010 DC3 0010011 3 0110011 S 1010011 S 1110011 DC4 0010100 4 0110100 T 1010100 t 1110100 NAK 0010101 5 0110101 U 1010101 u 1110101 SYN 0010110 6 0110110 V 1010110 v 1110110 ETB 0010111 7 0110111 W 1010111 w 1110111 CAN 0011000 8
23. that the secondary storage relies on the physical movement of the recording medium or a reading head In the secondary storage devices the movement takes longer than the data transfer and the retrieval time varies depending on the physical location of the next item Why software is stored on ROM 1 Software in ROM does not have to be loaded in RAM and is readily available and accessible by the processor when the power is turned on in the computer Page 50 of 115 WwwW revision notes co cc i3 a 2 This software is not supposed to be altered or upgraded Why it is important that ROM has some characteristics of RAM Processor can only access data held in the primary storage and ROM and RAM are both parts of the primary memory Data in ROM needs to be accessed randomly otherwise the data access would be too slow How secondary storage or backing stores are categorized Secondary storage can be categorized according to 1 Medium whether magnetic or optical 2 Technique used to store data whether data can be stored sequentially or for direct access 3 Capacity how much data can be stored 4 Portability whether it can be moved around easily 5 Access time to the data Backing Stores Magnetic tape This can only be used to store data sequentially but not direct access This is a disadvantage because it is largely unsuitable for many data handling applications which need to perform search for data based on direct acc
24. the bus cable has its other end connected to a port on the hub Terminator Bus Cable L Terminator Port on Hub Hup Advantages of bus topology Page 73 of 115 WwwW revision notes co cc RN gt Easy and inexpensive to set up as it requires the least amount of cables compared to other topologies gt Easy to add nodes without disrupting the network Disadvantages of bus topology gt The whole network goes down if the main bus cable fails at any point gt Cable failure is difficult to isolate gt Network performance degrades as the number of computers increase and the network is heavily used Star Topology In star topology each node is connected to a central computer which controls the network Central Computer Workstation 4 Advantages of star topology Workstation 7 Workstation 2 Workstation 6 Workstation 3 Workstation 5 gt Ifone cable fails the other nodes are not affected gt Network performance does not degrade as the number of computers increase and the network is heavily used because each computer has its own cable connecting to the server gt Reliable market proven system gt Easy to add and remove nodes without disrupting the network Disadvantages of star topology gt Costly to install because of the length of cables required gt Ifthe central computer crashes the whole network goes down Page 74 of 115 Www revision notes co cc
25. user enters data to the program and interacts with it Variables A variable is one or more memory locations which can store data A simple variable can carry only one piece of data at a given instance A data structure such as an array can carry more than one data at a given time The number of data that an array can carry at a given time is determined by the size of the array A variable must be declared before it is used in a program When a variable is declared in a program its name and the data type should be specified in the declaration statement Simple variable In Visual Basic a simple variable such as StudentName is declared as Dim StudentName as String Page 17 of 115 wWww revision notes co cc 2 RN StudentName is the name of the variable and String is the data type of the variable The data John can then be assigned to the variable as follows StudentName John When another piece of data Peter is assigned to the variable the previous data John will be replaced by the new value StudentName Peter Array varibales In Visual Basic an array variable is declared as follows Dim StudentNameArray 1 To 100 As String This means that The name of the array is StudentNameArray The array can contain up to a maximum of 100 pieces of data i e it can contain up to 100 student names The array can contain only data that have String data type Each piece of data in the array is identi
26. 0111000 X 1011000 X 1111000 EM 0011001 9 0111001 Y 1011001 y 1111001 SUB 0011010 0111010 Z 1011010 Z 1111010 ESC 0011011 0111011 1011011 1111011 FS 0011100 lt 0111100 1011100 1111100 GS 0011101 0111101 1011101 1111101 RS 0011110 gt 0111110 1011110 1111110 US 0011111 0111111 _ 1011111 del 1111111 What is EBCDIC system e EBCDIC stands for Extended Binary Coded Decimal Interchange Code e EBCDIC system is used in mainframe computer to represent data as text e It uses 8 bits to represent each keyboard character Array An array is a data structure which consists of a set of adjacent memory locations and can hold only a defined number of data items es eS es ee Record 1 Record 2 Record 3 Record 4 The array has to be initialized before it is used in a program Initializing means declaring the e Name of the array e Data type of the array e Maximum number of data items that can be contained in the array size of the array In Visual Basic an array that would hold a maximum of 100 student names can be initialized as Dim StudentNameArray 1 to 100 as String Page 32 of 115 WwwW revision notes co cc The data can be assigned to the array as following StudentNameArray 1 John StudentNameArray 2 Peter StudentNameArray 3 Michael It is incorrect to indicate a data item as StudentNameArray 0 because the indexes of the array start from 1 but not f
27. 15 Www revision notes co cc RN Disadvantages of using a network of computers over using a collection of stand alone computers Users become dependent on them For example if the network file server develops a fault then many users will be unable to run application programs On many sites a back up file server can be switched into action if the main server fails Ifthe network stops operating then it may not be possible to access various hardware and software resources The efficiency of a network is very much dependent on the skill of the network administrator A badly managed network might operate less efficiently than a set of stand alone computers It is difficult to make the system secure from hackers novices and industrial espionage As traffic increases on the network the performance degrades unless it is properly designed Network topology Network topology is the physical layout of network nodes Bus topology star topology and Ring topology are the widely used topologies of local area networks Bus Topology All the devices on the network share a single cable known as the bus cable Each node is independently attached to the common bus cable Data can be transferred from any computer to any other computer The bus cable ends at a terminator which absorbs electrical signals so they don t bounce or reflect back and forth on the bus The bus cable is located inside a hub and each piece of cable connected to
28. 50 349 9839349 Position 351 349 6315349 Position 452 452 7948452 Position 665 665 7005665 Position 666 666 0108666 Position 667 667 0000667 Position 668 666 9552666 Position 669 666 5715666 Position 999 999 2167999 Then the hash table would be as given below Position in the hash table Hash Key Position O 000 Position 1 001 Position 2 999 Position 114 114 Position 115 114 Position 116 115 Position 243 243 Position 244 243 Position 245 243 Position 348 348 Position 349 349 Position 350 349 Position 351 349 Position 452 452 Position 665 665 Position 666 666 Position 667 667 Position 668 666 Position 669 666 Position 999 999 Page 45 of 115 WwwW revision notes co cc 19 RN How does the program create the hash table by writing the hash keys to an overflow area when a collision occurs When a collision occurs occurrence of the same hash key at the same position of the hash table the program writes the second instance of the hash key to an overflow area If a second collision occurs with the same hash key the program writes the third instance to a second overflow area and so on It means that the preceding instance keeps a pointer to the next instance in the next overflow area The hash table would be as given below
29. 6 0000667 0000114 9794004 3421999 5443115 1414243 9552666 4119349 Page 43 of 115 WwwW revision notes co cc 5715666 9839349 6869348 6315349 For each primary key apply the hash function h key key MOD 1000 This will give the following hash keys for each primary key Primary Key Hash Key 5219243 243 7948452 452 4523001 001 7005665 665 4298114 114 5358243 243 2167999 999 0108666 666 0000667 667 0000114 114 9794000 000 3421999 999 5443115 115 1414243 243 9552666 666 4119349 349 5715666 666 9839349 349 6869348 348 6315349 349 iTe How does the program create the hash table by writing the hash keys to the next available free location when a collision occurs If another hash key has already occupied that location of the hash table the program writes the second instance of the hash key to the next available disk address Position in the hash table Hash Key Primary Key that the hash key is pointing to Position 0 000 9794000 Position 1 001 4523001 Position 2 999 3421999 Position 114 114 4298114 Position 115 114 0000114 Position 116 115 5443115 Position 243 243 5219243 Position 244 243 5358243 www revision notes co cc Page 44 of 115 18 Position 245 243 1414243 Position 348 348 6869348 Position 349 349 4119349 Position 3
30. A translator program converts source code written in a high level programming language to machine code 2 Translator programs are of three kinds Compilers Interpreters and Assemblers What are utility programs 1 Utility programs are routines added to the operating system to carry out common tasks in the computer system such as that control output to the printer and storage of data 2 Examples for utility programs are Disk formatter File handler Hardware or device driver File compressor Virus checker Examples of utility programs 1 Disk formatter Deletes the data already on the disk and divides the surface of the disk into tracks and sectors 2 File handler Manages files stored in a computer system For example saving a file and finding a file Page 10 of 115 WwwW revision notes co cc 3 Hardware or device driver Gives the instructions necessary to control communication between the processor and a peripheral device 4 File compressor Reduces the size of a file without the loss of any details in it so that the transmission of a very large file can be done faster 5 Virus checker Checks any files entering a computer system for viruses and delete the virus before it can damage files What is a library 1 A library is a collection of components used to develop software 2 A library is different from an executable in that it is not an independent program but only a Component a component is a compiled routine or
31. Disadvantages of form based user interface 1 User needs training to understand how to use the program 2 User needs training to understand what data to be inputted Menu Based User Interface Description of menu based user interface 1 It contains a series of options from which the user selects 2 The selection of an option may lead to a sub menu 3 It is usually used with touch sensitive screens Examples The interface of the ATM machine and the interface at restaurants like McDonalds Advantages of menu based user interface 1 The system is self understandable and the user does not need training 2 This can be used in situations where the operator tends not to know what options are available Page 103 of 115 www revision notes co cc 3 No need to implement data validation rules as the system can make the user always input correct data by restricting choices for the user 4 Menu based interface can be used with touch screens to implement systems in very busy environments or where many people are waiting to use the system such as in factories restaurants railway stations and airports 5 Menu based interface is used with touch screens to facilitate many computer illiterate people who would use them Disadvantages of menu based user interface 1 The system takes time to find information as the user has to go through many screens before the system outputs the results Example of a menu based system system at a railway sta
32. MOD 1000 876 52002 MOD 1000 002 Page 42 of 115 www revision notes co cc 16 What are the criteria to go by when choosing a hashing algorithm e It should be able to generate any of the available addresses on the file e It should be fast to calculate e It should minimize collisions e It should give a good spread of records Methods used to overcome collision Method 1 Writing the hash key to the next available free location The computer program which writes records to the random access file writes the hash keys to the hash table serially If a collision occurs the program writes the hash key to the next available free location in the hash table and the record is written to the memory address pointed by the hash key Method 2 Writing the hash key to an overflow area The computer program which writes records to the random access file writes the hash keys to the hash table serially If a collision occurs the program writes the hash key to the corresponding location in an overflow area and sets a pointer from the location in the hash table where the collision occurred to the location in the overflow area The record is written to the memory address pointed to by the hash key An illustration of how a program creates a hash table and handles collisions Following are the primary keys of the records which are supposed to be written to a random access file 5219243 7948452 4523001 7005665 4298114 5358243 2167999 010866
33. RN Chapter 1 1 Components of a Computer System and their Uses A computer information system generally carries out the following tasks Primary Storage Data Information Data Information Information Process Data Information Data Information Backing Storage A computer information system consists of hardware software and live ware What is hardware Hardware is the physical parts parts which can be seen and touched of a computer system They are Input devices devices used to enter data to the system such as keyboard mouse and scanner 2 Output devices devices used to output information from the system such as monitors printers and speakers 3 Storage devices devices used to store programs data and information Storage devices are of two kinds Primary storage This is also called RAM random access memory It stores currently running operating system application programs and data files Secondary storage This stores programs data and information for future use Examples are hard disks CDs magnetic tapes flash drives etc 4 Communication devices devices used to transmit data between computers in a network such as modems ISDN adaptors network interface cards bridges and routers What is software Page 1 of 115 www revision notes co cc 2 RN 1 Software is a set of instructions coded in a programming language which tells the computer s process
34. a set of routines which carries out a specific task or a set of tasks and which does not have a user interface 3 A library can be linked to an executable either in runtime or compile time Why an operating system is likely to be stored on a backing store rather than in the memory of the computer 1 Usually the operating system requires a large amount of storage space 2 It allows for easy upgrading or changing from one system to a different one What is batch processing Batch processing means collecting data during a specific time period and processing them as one batch in one run without the intervention of the user during the processing of data How batch processing can overcome speed mismatch e Inthe computer the processor carries out its tasks at extremely high speed the peripherals carry out the tasks at a much slower speed compared to the processor and the user performs tasks at the slowest speed e The above difference in speed is known as the speed mismatch between the operator peripherals and the processor e Therefore in this situation the speed of data processing depends on the speed at which the user interacts with the computer which is very slow Page 11 of 115 Www revision notes co cc a RN e Batch processing puts the user off line i e processing occurs without the intervention of the user and thereby making the speed of data processing depend only on the speed of the processor and thereby overcome the s
35. ain Injury or RSI Page 110 of 115 Www revision notes co cc a RN RSI is a collective name for a variety of disorders affecting the neck shoulders and upper limbs It can result in numbness or tingling in the arms and hands aching and stiffness in the arms neck and shoulders and an inability to lift or grip objects Some who suffer from RSI cannot pour a cup of tea or type a single sentence without excruciating pain How can using the computers cause eyestrain in an employee at his workplace Computer users are prone to eyestrain from spending long hours in front of a screen There is no evidence that computer use causes permanent damage to the eyes But glare improper lighting improperly corrected vision through not wearing the correct prescription glasses poor work practices and poorly designed workstations all contribute to temporary eyestrain What ergonomic environment should be supplied by an employer to his employees Ergonomics refers to the design and functionality of the environment and encompasses the entire range of environmental factors Employers must give consideration to 1 Lighting The office should be well lit Computers should neither face windows nor back onto a window so that the users have to sit with the sun their eyes 2 Furniture Chairs should be of adjustable height with a backrest which tilts to support the user at work and at rest and should swivel on a five point base It should be at a correct h
36. ange the pointer of the new data to point to the current data ELSEIF current data first data set the pointer of the new data to point to the current data set START pointer to point to the new data ENDIF ELSEIF End Of List has reached and new data gt current data set the pointer of current data to new data set the pointer of new data to NULL Page 34 of 115 Www revision notes co cc ENDIF set NEXTFREE pointer to point to the next free location ENDIF Algorithm 2 Deleting an item from a linked list REPEAT READ data from the linked list by following the pointers IF current data data to be deleted THEN set the pointer of the previous data to the next data add the current data to the free list and ENDIF Algorithm 3 Searching for an item in a linked list REPEAT READ data from the linked list by following the pointers IF current data searched THEN DISPLAY message A match is found STOP ENDIF UNTIL end of the list IF current data lt gt data searched THEN DISPLAY message A match is not found STOP ENDIF Stack Stack is a list of items where Stack Pointer SP e Data are both pushed to and popped off from the top of the stack e Last item in becomes the first item to be out LIFO A stack needs one pointer because adding data to the stack and popping data off the stack are done at the same end which is called the Top of the stack The Stack Pointer SP points to the top of the stack Que
37. aphs Ideal for showing trends Reports in text form Gives exact details or Page 100 of 115 Www revision notes co cc 4 figures Reports in tabular form Arranges exact details to make them simpler to interpret Interactive presentations Allows the manager to tailor the output required Sound Can inform while the manager is attending to some other task What is timeliness This is the concept that the data changes over time and that data is only a part of a sensible solution for a short period of time before it becomes outdated The data on heart rate 3 hours ago is not of any importance to the nurse looking after a patient But that data is very important to the doctor in providing a clue as to the reason for the sudden change in the heart rate What is relevance of data This means that the data has a bearing or use in a particular application For example the date of birth of a customer of a food catering company has no relevance to the system Page 101 of 115 www revision notes co cc Chapter 1 10 Designing the User Interface Why good user interface design is an important part in system design l 2 3 It avoids ambiguity in data entry It allows the user to input all the data It presents the output in an easily understandable way Factors that the analyst should consider when designing an HCI for data input l 2 3 4 Who will be using the
38. archived 6 To use for taxation purposes 7 To produce management information Page 48 of 115 wWwww revision notes co cc Chapter 1 5 Hardware Components of the processor Three main components of the processor are control unit arithmetic and logic unit and memory unit Functions of the control unit are 1 Decides which instruction to carry out next and then go and fetch it 2 Determines what needs to be done to carry out the instruction decodes the instruction 3 Manages the execution of the instruction by telling other parts of the processor what they should do to carry out the instruction 4 Choreographs the instruction cycle by using a clock Functions of the arithmetic and logic unit are 1 Contains circuitry that allows it to carry out arithmetic 2 Performs logical decisions 3 Acts as the gateway between the processor and the peripheral devices of the computer system such as the hard drive Functions of the memory unit are 1 Stores the operating system or parts of the operating system 2 Stores application software instructions that are currently being used in the computer 3 Stores the data files that are currently being used in the computer Data storages in a computer Data storages in a computer are divided into two categories 1 Primary storage or main memory 2 Secondary storage or backing store What is primary storage or main memory This is the storage that can be accessed by the compute
39. ardware and software for a particular layer of protocols When files containing only text data are transmitted in a network they are sent at a slower bit rate because the text data are not time sensitive When files containing pictures graphics and animations are transmitted in a network they have to be sent at a higher bit rate because those data are time sensitive Data compression When files containing data other than text data is transmitted in a network it is important to limit the amount of data that is being transmitted Unlike text data the graphics videos and animations need a large amount of bits to be coded This will decrease the speed of data transmission of files containing graphics videos and animations and hence the time it takes to download the file at the destination computer Speeding up the transmission of a file by reducing the number of bits in the file is known as data compression Reducing the number of bits in a file is done by encoding the data using fewer bits The receiving computer must decode the data in order to understand it Compressed data communication works only if both the sender and receiver understand the encoding scheme Compression is useful because it helps reduce the consumption of expensive resources such as hard disk space and bandwidth of data transmission The disadvantage of data compression is that the data must be decompressed to be used and this extra processing may be detrimental to some ap
40. at the programmer s site 4 Beta Testing Testing carried out by the intended users of the program at the users site Selection of Test Data The data used to test a program are divided into the following three types 1 Valid Data Page 22 of 115 wWww revision notes co cc 2 RN Valid data are accurate and reasonable data within the context of the program which produce correct output Valid data is used to test whether the program would produce the expected outcome when valid data is entered Examples of valid data which can be used to test a program which processes exam marks to evaluate the grade for mathematics at a school exam are 79 92 44 12 etc 2 Extreme Data When valid data falls within a specific range the borderline data are called extreme data Examples of extreme data which can be used to test a program which processes exam marks to evaluate the grade for mathematics at a school exam are 0 and 100 3 Invalid data These are the data which are inaccurate and unreasonable within the context of the program Examples of invalid data which can be used to test a program which processes exam marks to evaluate the grade for mathematics at a school exam are 47 and 127 Debugging Tools and Techniques 1 Translator diagnostics When the source code is translated the translator looks up the reserved words of the programming language in a dictionary If the word is spelt incorrectly or has not followed the rules o
41. ave changed from 1 to 0 But the parity of the byte still remains as even Page 81 of 115 Www revision notes co cc Chapter 1 7 System Development Life Cycle System development life cycle Maintenance Problem Definition Implementation Development System Development Lifecycle as an iterative process 1 Need for a change in the system once it has been developed has to be handled by defining and analyzing the requirements which takes the development process back to the beginning of the life cycle 2 The SDLC is an iterative process because each stage relies on the following stages as well as the previous ones Tasks performed in the SDLC SDLC Phase Things done Analysis Fact finding Page 82 of 115 Www revision notes co cc 2 Analysis of facts using system flowcharts DFDs cause and effect diagrams Requirements specification Consideration of alternative solutions Design Describing the objectives Project plan and schedule Specification of the data input and output data types and methods of input and output Specifying the file structure Specifying the algorithms used for data processing Specifying the hardware and software Designing the test plan Development Coding the program or customizing a software package Testing Conducting tests to check the data validation routines Conducting tests to check functiona
42. c 4 Form should be restricted to one sheet 5 Form should not be folded 6 Form should be kept clean 11 Barcode reader Used to input data included in a barcode to a computer The barcode consists of a series of alternating dark and light colored lines The thickness of the line identifies a specific character 12 MICR Magnetic Ink Character Reader Used to scan bank checks and input data printed with a special magnetized ink at the bottom of the check 13 Digital camera Used to input photos taken and stored in its memory to the computer s memory 14 Web Cam Used in video conferencing weather stations and checking on children in nurseries 15 Sensors Used to input signals coming from sources in monitoring and control systems and data logging system 16 Microphone and Voice Recognition Used as an input device in voice recognition systems by speaking directly to the computer 17 Graphic tablet or digitizer A Graphics tablet consists of a flat surface upon which the user may draw an image using an attached stylus a pen like drawing apparatus The image generally does not appear on the tablet itself but rather is displayed on the computer monitor This uses a cursor to trace over a technical drawing put on a flat surface called the tablet When the user draws on the paper the tablet senses where the pencil is pointing and transfer the line to the screen Page 57 of 115 WwwW revision notes co cc 10 18
43. cluded between the ALU and the secondary storage This breaks the exchange of data between the primary memory and the secondary storage into two stages Page 52 of 115 WwwW revision notes co cc Stage 1 Filling the buffer from the processor Primary Memory gt gt Secondary Storage Stage 2 Emptying the buffer to the secondary storage Primary Memory lt gt Secondary Storage When the secondary storage device has used up the contents of the buffer it needs to tell the processor that it requires more data This is done by sending a message to the processor which is called as an interrupt Definition of an interrupt It is a signal generated by a process a running instance of a software application or a hardware device to get the attention of the processor Summary of the mechanism of data transfer between the processor and a secondary storage using buffers and interrupts 1 Processor transfers a whole block of data from the primary memory to the buffer at once 2 The buffer transfers data one by one to the backing store slowly 3 In the meantime the processor can attend to some other task in the computer 4 When the buffer becomes empty the backing store sends an interrupt signal to the processor to signal the fact 5 According to the priority of the job handling the interrupt the processor decides whether to suspend the current job and to carry out the interrupt or to store the interrupt for execution later
44. data where the human expert might respond Don t know 2 Delivers advice 3 Explains reasoning to the user Components of an expert system 1 Knowledgebase Contains storage of facts collected and provided by number of experts in the related field 2 Rule base Contains algorithms used to interpret the information in the knowledgebase 2 Inference engine Computer program which applies rules in the rule base on the facts in the knowledgebase to extract information 3 User interface Interface used by the user to interact with the expert system Examples of expert systems 1 Oil exploration system 2 Navigation system to find the most appropriate route to a given destination 3 Diagnosis system for medical conditions vehicle defects and faults in pipelines etc How an expert system is set up 1 Knowledgebase is created by collecting facts from number of experts 2 Rule base is created by experts in the field 3 Inference engine is developed by programmers 4 User interface is developed by the programmers to suit the users How an expert system is used 1 The system tries to match data or patterns with the knowledgebase 2 The system uses rules to interpret the matching data and the patterns found 3 The system produces reasons and advices Page 108 of 115 wWww revision notes co cc Chapter 1 12 Implications of Computer Use State the advantages gained by the employees of a company by using c
45. ded from an e commerce Web site in order to purchase an item Single user systems A single user system and its programs can be used by only one person at a time An example of a single user system is the personal computer PC used at homes Most single user systems are multi tasking Multi tasking systems This is an operating system which allows several application programs to be run at the same time Even though it appears that more than one task is running simultaneously it does not actually happens What really happens is that the processor switches processing between the application programs in very quick time Page 13 of 115 wWww revision notes co cc Multi user systems This is an operating system which services more than one user simultaneously Example of a multi user system is a mainframe computer which services many users who are connected to it through terminals that have very little or no processing power Distributed systems This is a system which uses many storage locations on different computers to store software and data files in a network environment Advantage of a distributed system Advantage of a distributed system is the ability to access data files quickly and to run programs quickly because more than one file handling command can be carried out at a time Disadvantage of a distributed system Disadvantage of a distributed system is the complexity of maintaining the security of the system User inter
46. ea covered by them A network that covers a small geographical area is called a local area network or a LAN Examples for local area networks are the networks in schools offices and factories A network that that covers a wide geographical area is called a wide area network or a WAN Examples for wide area networks are the networks in companies which have branches in many cities or countries The Internet is the largest wide area network How LANs differ from WANs LAN WAN LAN exists in a small geographical area WAN exists in a wider geographical area LAN is usually hard wired uses cables to WAN requires other transmission media to connect computers connect devices except for cables Data in a LAN is easier to keep secured Data in a WAN is prone to hacking Computers in a LAN can share hardware such Computers in a WAN cannot share hardware as printers such as printers Hardware and software needed for communication in a LAN gt Network interface card which is needed by the computers to get connected to each other Page 71 of 115 Www revision notes co cc Cables which are used as the transmission medium Hub which is used to concentrate the cables connected to the computers Network operating system which is needed by the computers to get connected to each other and communicate data and information Hardware drivers for the network interface card and the modem which are needed to convert data and information
47. eck the errors Annotation Help given to understand code within the code itself is called annotation The following are the common ways of annotating code 1 Indentation of program code By indenting the code within a programming construct with a fixed number of spaces Examples are the code within a Procedure a Function an IF THEN ENDIF construct SELECT ENDSELECT construct DOWHILE ENDWHILE construct FOR NEXT construct etc 2 In line comments The comments written within the code itself is known as in line comments Programming languages have different rules of writing in line comments For example in Visual Basic an in line comment must start with a single quote character 3 Use of meaningful names for variables Naming the variable that carries the value of the customer s name as CustomerName instead of ayy just naming it as x Page 24 of 115 Www revision notes co cc 4 Dividing the program code into modules The code that carries out a specific task can be written as a separate module Advantages of annotation 1 It helps in following the solution or the algorithm of the program 2 It helps in understanding the code easily and thereby improves the maintainability of the program 3 It helps in reducing the errors in the program 4 It helps in documenting the program 11 Algorithms An algorithm is a sequence of step by step instructions for solving a problem Two ways of pre
48. ed by computer literate people Graphical User Interface Description of GUI 1 It contains windows icons menus and uses mouse pointer to interact with the computer 2 The GUI is used by selecting options from menus of choices and from a set of small pictures which represent the different options available 3 Choices are selected by using some sort of pointing device such as a mouse Example Interface of the Microsoft Windows Desktop program and the Control Panel program Advantages of GUI 1 Easy to understand the interface as it includes pictures and graphics 2 Easy to learn the system as it has no commands to memorize Disadvantages of GUI 1 Some icons on the GUI may be unfamiliar and confusing Natural language user interface The computer asks questions which elicit a response which gives the user the impression that he is talking to the computer Page 105 of 115 Www revision notes co cc Chapter 1 11 Characteristics of Information Systems What is a passive information system This is an information system from which information can be obtained but where the data cannot be changed An example for a passive information system is a computerized dictionary Here the user can search to find the meaning of a word but he cannot change the contents of the dictionary What is an interactive information system This is an information system where the user can alter the data as well as can obtain information
49. eight relative to a keyboard on the desk 3 Work space The combination of chair desk computer accessories such as document holders mouse and mouse mats paper trays and so on lighting heating and ventilation all contribute to the worker s overall well being 4 Noise Noisy printers for example should be given covers to reduce the noise or located in a different room 5 Hardware The screen must be tilt and swivel and be flicker free The keyboard must be separately attached 6 Software Software is often overlooked in the quest for ergonomic perfection The EEC directive made a clear statement about the characteristics of acceptable software requiring employers to analyze the tasks which their employees performed and to provide software which makes the tasks easier It is also expected to be easy to use and adaptable to the user s experience Social and ethical effects of the Internet 1 Chat rooms have created a new type of social circle 2 Generally inappropriate sites such as pornographic sites emerge Page 111 of 115 Www revision notes co cc 3 Danger to the structure of the society because of the emergence of abnormal views 4 Religion is undermined 5 Exposes people to new contradictory views 6 Sites that encourage breaking of law emerge 7 Sites giving incorrect information appear What are the advantages of having unrestricted access for the students to the Internet 1 Allows communicati
50. em EBCDIC system etc Denary System Denary system is made up of powers of 10 RN Position 8 Position 7 Position 6 Position 5 Position 4 Position 3 Position 2 Position 1 Value 107 10 10 10 10 10 10 10 10 000 000 1 000 000 100 000 10 000 1 000 100 10 1 Binary Number System Binary number system is made up of powers of 2 Position 8 Position 7 Position 6 Position 5 Position 4 Position 3 Position 2 Position 1 Value 2 2 2 2 2 i 7 2 128 64 32 16 8 4 2 1 Conversion of data between denary and binary systems Examples 1 Convert denary number 117 to the corresponding binary number using an 8 bit register 117 58 29 14 NININININJIN elelo elole Answer 01110101 2 Convert binary number 10110110 to the corresponding denary number www revision notes co cc Page 28 of 115 Denary 128 64 32 16 8 4 2 1 Binary 1 0 1 1 0 1 1 0 Answer 128 32 16 4 2 182 Binary numbers represented by storage locations of different sizes Size of Storage Smallest Largest Positive Data Positive Data 1 Byte 0 11111111 255 2 Bytes 0 1111111111111111 65535 Largest data that can be stored in a storage location of the size 2 bytes is calculated as follows 14 24 4 8 16 32 64 4 128 256 512 1024 2048 4096 8192 16384 32768
51. en case e f used only as a master file the organization has to be sequential e If itis a transaction file the organization is either serial or sequential e f used as a master file as well as for direct access the organization has to be index sequential e f used only for direct access the organization can be either random or index sequential What it means by backing up a file Backing up means creating an extra copy of a file to protect data if in case the original file get corrupted or destroyed What it means by archiving a file Archiving a file means making a copy of little used data at a certain point of time for long term storage so that it can be removed from the main file to make space for other data Backup procedure 1 Create several backup copies on tapes or on other portable storage media such as rewritable CDs or zip drives at sensible and regular time intervals 2 Backup copies are transported to and stored at locations away from the location of the original file 3 If applicable keep a copy of the transaction file between backups Why it is necessary for a company to archive a file 1 The file s hit rate has reduced 2 Many records of the file are not used 3 Necessary to free up space in the hard drive 4 Necessary to store example states of the file before lost forever Page 47 of 115 Www revision notes co cc 21 5 Replacing the old file with a new file leads to old files being
52. ers It allows sharing of data and information held in one computer accessible to many users Page 62 of 115 Www revision notes co cc a RN e Itis easier to store application programs on one computer and make them available to all users rather than having copies individually installed on each computer It allows sharing of a centralized database It allows electronic mail and messages to be sent between users It allows the implementation of centralized security It is easier to set up new users and equipment It allows the connection of different types of computers which can communicate with each other What are the disadvantages of using a network of computers over using a collection of stand alone computers e Users become dependent on them For example if the network file server develops a fault then many users will be unable to run application programs On many sites a back up file server can be switched into action if the main server fails e Ifthe network stops operating then it may not be possible to access various hardware and software resources e The efficiency of a network is very much dependent on the skill of the network administrator A badly managed network might operate less efficiently than a set of stand alone computers e It is difficult to make the system secure from hackers novices and industrial espionage e As traffic increases on the network the performance degrades unless it is properly desig
53. es co cc 9 Disadvantages of buying an off the shelf software package 1 Features specific to the organization may not be available 2 Software may not run on the existing hardware Hardware used to enable computer systems to communicate or communications hardware 1 Network interface card This is a device installed in a slot on the motherboard which is used to connect two computers One end of a network cable is attached to a port on the network interface card 2 Modem This is a device installed in a slot on the motherboard or attached to the computer externally by a cable which is used to convert digital data coming from the processor to analog before it enters the telephone lines and to convert analog data coming along the cable to digital before it enters the computer The telephone cable is connected to a port on the modem Page 9 of 115 www revision notes co cc Chapter 1 2 System Software What are the types of system software 1 Operating system 2 Translator programs 3 Utility programs 4 Library programs What is an operating system 1 Operating system is a software program which controls the operations of the computer system 2 It provides a user interface 3 It controls how the computer responds to user s requests 4 It controls how the hardware communicate with each other 5 It provides an environment in which application software can be executed What is a translator program 1
54. ess Access time to data is also very long because data has to be accessed sequentially However the data storage capacity is high and the tape is freely portable It is very useful for producing backup copies of files Magnetic tapes are used for storing backup copies of files Floppy disk Floppy disk can store data for direct access Storage capacity is very small Very portable and can be handled easily because of its small size and the protective jacket Data access time is very slow because of the limited speed of rotation and the relatively crude nature of the read heads Floppy disks are used for transferring confidential data files Hard disk Hard disk can store data for direct access Data storage capacity is very high Access time is very fast because the hard disk rotates very fast Hard disks are portable but they are mostly used as stationery devices in the computer system Hard disks are used to store large operating systems databases large number of graphics and images etc Page 51 of 115 wWww revision notes co cc CD ROM CD ROM is an optical storage device It uses the reflection of a laser beam off a pitted surface to store data CD ROM can be used to store data for direct access Data storage capacity is high CD ROMs are very portable Access time to data is fast The data stored in CD ROMs cannot be changed Therefore CD ROM is used to store data such as operating systems application software packages and large data
55. etween two devices but only one direction at a time Simplex mode of transmission means passing data only in one direction between two devices Examples 1 The data transmission between the primary memory and the hard drive of the computer is half duplex 2 The data transmission between the computer and the printer is half duplex because the computer transmit data files to the printer for printing and the printer passes messages to the computer such as error messages Bit rate Number of bits that can be sent in one second is known as bit rate The unit used to measure the bit rate is Baud 1 Baud 1 bit per second What is the relationship between the bit rate and the way that the data in the files are used 1 When files containing only text data are transmitted in a network they can be sent at a slower bit rate because the text data are not time sensitive 2 When files containing pictures graphics and animations are transmitted in a network they have to be sent at a higher bit rate because those data are time sensitive 3 When files other than the ones containing only text data is transmitted in a network it is important to limit the amount of data that is being transmitted This will increase the speed of data transmission and therefore the time it takes to download the file at the destination computer will decrease Speeding up the transmission of a file by reducing the amount of data is known as compression Why bit ra
56. eue is empty STOP ELSE Set data in the cell pointed to by the head pointer to the variable item_deleted Increment the head pointer by 1 STOP ENDIF What is serial or sequential access This is the method used by a computer program to access a record in a file where each and every record is checked from the beginning of the file until a match is found What is direct or random access This is the method used by a computer program to access a record in a file directly without going through each and every record starting from the beginning of the file The computer program uses the mechanism called hash keys for direct access What is a serial file and how it is created This is a file where records are written to it in the order that they are received The records in a serial file may not be in order with respect to a key field Page 38 of 115 WwwW revision notes co cc 12 How a program access records in a serial file The program accesses the records sequentially A program cannot access records in a serial file directly What is a sequential file This is a file where records are organized in ascending or descending order with respect to the primary key How a program creates a sequential file The program writes a new record to the end of the file and sorts the file each time a new record is added How a program access records in a sequential file The program accesses the records sequentially A program
57. evices in the ring is disrupted Types of data transmission Data transmission can be divided into the following two types Serial transmission Parallel transmission Serial transmission is the transmission of data one bit behind another along a single wire eoe o o o o o o o Parallel transmission is the transmission of data along a set of several wires usually a multiple of eight wires where bits move simultaneously as a bit front Parallel transmission is faster than serial transmission Parallel transmission is less reliable than serial transmission because of the fine tolerances in the transmission as the bits can become muddled up Examples 1 The Data transmission between the primary memory and the hard drive of the computer is parallel because the processor requires the data to be downloaded as quickly as possible 2 The data transmission between the computer and the printer is parallel because the computer needs to send a big chunk of data to the printer s buffer quickly so that the processor will be free to attend to other tasks of the computer Modes of data transmission Data transmission can be divided into the following three modes e Duplex mode e Half duplex mode e Simplex mode Page 66 of 115 www revision notes co cc RN Duplex mode of transmission means passing data in both directions at the same time between two devices Half duplex mode of transmission means passing data in both directions b
58. evision notes co cc Page 26 of 115 ll UNTIL M 0 ENDWHILE M 0 if person is not in the room Algorithm for updating a master file with a sorted transaction file READ record from master file READ record from transaction file WHILE Not EOF transaction file IF primary key of master file primary key of transaction file Update master file READ next record from transaction file IF primary key of master file lt gt primary key of transaction file READ next record from master file ENDIF ELSEIF primary key of master file lt primary key of transaction file READ next record from master file ENDIF ENDWHILE Updating and backing up of a master file Back up master file 0 Encounter a rogue value 0 Add records to master file 0 Copy to new master file 0 o Change record in master file Delete record in master file t ter fil W W W O i vision notes co cc Read record from transaction file 0 Encounter a record key o Amend record in master file Chapter 1 4 Data Representation Structure and Management What is a character set This is the set of symbols that the computer s software can recognize How the character set is represented in the computer The character set is represented in the computer by using bit patterns The bit patterns are interpreted in different ways under different methods of data representation such as binary number system ASCII syst
59. executed until the syntax error is corrected 2 Logic Errors This is an error in the way that the program solution has been designed For example an instruction in the program may tell the processor to jump to another part of the program This is Page 21 of 115 wWww revision notes co cc s RN fine as long as the instruction tells the processor to go to the right part of the program If it tells the processor to go to the wrong place the program will not produce the expected result Unfortunately a logic error does not usually prevent a program from executing it just make the program produce wrong results Another example of a logic error is when an incorrect formula is used such as Net Salary Gross Salary Tax This produces wrong results for Net Salary The correct formula should be Net Salary Gross Salary Tax 3 Arithmetic Errors This is an error caused by inappropriate arithmetic This is sometimes thought of as a type of logic error but is rather different because the computer is asked to do something that is impossible A good example is when it is coded to divide by 0 This is impossible and would cause the program to fail Testing Methods 1 White Box Testing Testing all possible routes through the program logic is called white box testing 2 Black Box Testing Testing performed to check whether the results are as expected as for a given input 3 Alpha Testing Testing carried out by the programmer
60. f the programming language a message detailing the error and hints about correcting the error is displayed to the programmer These messages are called translator diagnostics 2 Cross referencing Identifying errors caused by duplicate variable names 3 Traces Tracing the values of variables through a program run as each instruction is executed This way the values can be checked to see where they suddenly change or take on an unexpected value 4 Variable dumps This is the display of the values of all the variables at a specified part of a program This enables the programmer to compare those values with the expected results 5 Desk checking dry run Page 23 of 115 wWww revision notes co cc a RN The programmer works through the logic in the program code manually keeping track of the values of the variable Since programs contain a large number of instructions usually only small segments of code that the programmer suspect of containing an error is dry run 6 Break points This is to stop execution at significant points in the source code 7 White box testing Testing all possible routes through the program logic is called white box testing 8 Black box testing Testing performed to check whether the results are as expected as for a given input 9 Bottom up programming Building a program by writing code to use a set of components is called bottom up programming The code in these small modules enables it easy to ch
61. face This is the means of communication between the user and the computer system and consists of both hardware and software Form based user interface 1 This is an on screen form which contains specified areas to enter data such as boxes drop down boxes check boxes option buttons etc 2 The user interface has a cursor which can be moved to the next area to be filled in with data 3 When data is entered to the specific areas it will be validated before it is processed How the form based user interface is used 1 It prompts the operator to ask questions 2 It makes the operator input the data in correct order 3 It makes the checking of the data easier Page 14 of 115 Www revision notes co cc Menu based user interface 1 Menu based user interface has a list of choices made available to the user followed by a further set of choices based on the first choice and so on until the result is obtained 2 This is used in situations where the operator tends not to know what options are available 3 Input is often done using a touch screen because of the location of such systems For example menu based systems are used in very busy environments or where many people are waiting to use the system such as in factories restaurants railway stations and airports 4 Input is often done using touch screens to facilitate many computer illiterate people who would use them Example of a menu based system system at a railway station
62. fied by a unique index The first piece of data in this array is StudentNameArray 1 the second piece of data is StudentNameArray 2 and so on up to StudentNameArray 100 It is wrong to code as StudentNameArray 0 because the indexes fall within the range of 1 to 100 but not from 0 to 99 Depending on where the variable is declared in the program the variable s scope is determined The variables can be identified according to their scope as given below e Local variables e Global variables Local Variables Local variables are declared within a procedure or a function Therefore a local variable can be accessed only by the code within that procedure or function Global variables Global variables are declared in the main program or in a public module of a program This means that the code anywhere in the program can access a global variable Page 18 of 115 WwwW revision notes co cc Procedures and Functions A procedure carries out a specific task and may or may not return a value to its calling statement A function carries out a specific task and always returns a value to its calling statement A procedure or a function has to be called by a statement or an expression in order for it to execute The value returned by a function is contained in the name of the function The function then returns the value to its calling statement Therefore the calling statement of the function must be a part of an expression A val
63. g the computers ina LAN images using JPEG technology Page 99 of 115 Www revision notes co cc 2 8 To find the arrival time of the next bus at a bus Touch screen Halt What are the common methods of output l Text Example Text information displayed on a form based user interface such as the total cost of an order Graphs Example Temperature variation during a month Charts Example Annual sales figures of a company on a monthly basis Reports Example Marks and grades obtained by the students of a class in a school Interactive presentations Example CEO of a company participating in a videoconference Sound Example Voice synthesis for reporting to blind people Burglar alarm system Video Example Demonstration of performing an experiment in the chemistry lab Images Example An online album containing the picture of cars at a car dealer A database of criminals Animations Example Used in a slide based presentation to eliminate boredom Method of output according to the target audience Target Audience Method of output 1 A nurse working in an intensive care ward Sound of an alarm flashing light monitor screen showing a scrolling graph about the state of a patient s heart rate 2 A doctor who needs to diagnose whether a_ Fasting blood glucose level data of the patient patient has diabetes tested over several days 3 A manager of a business Gr
64. he output devices used at a point of sale are 1 Printer To print the till receipt 2 LCD To show purchase details and the cost of item 3 Buzzer To confirm the reading of the barcode Output Devices 1 Visual display unit standard TV standard computer screen Liquid Crystal Display A standard monitor includes a cathode ray tube CRT The resolution of the standard monitor is determined by the number of pixels in a given area on the screen 2 Printer Dot matrix Laser Ink Jet Dot matrix printers are called impact printers because they print by striking the paper through a carbon ribbon The letters are formed by a series of dots Laser printer operates by heating the paper and making the toner particles fuse to the paper in those locations which make the contour of the letters Ink jet printers operate by spraying liquid ink on the paper at identified locations to draw the letters and pictures 3 Microfiche This is a rectangular shaped film of plastic which is divided into tiny areas which can store a miniature image of a page of a document A book with even 500 pages can be stored in a microfiche card 4 Plotter This is used to draw and output fine graphics such as maps and building designs The advantages of plotter are 1 Can produce hard copy output 2 Can produce large scale printouts 3 Can produce high quality and accurate output 4 Can produce the output as the data is inputted 5 Voice synthesis or s
65. ication programs where those parts can share data and communicate data with each other easily For example the user can move a drawing done with the graphic designing part of an integrated package to the word processing part of that same package in order to add some text to a graphic Advantages of integrated packages 1 Data can be shared 2 Commonly used features of individual packages are available and can be used throughout the package 3 Common screen design common toolbars common menus and common icons can be used throughout the package 4 It is simple for the staff to learn 5 It is cheaper than buying individual packages separately Disadvantages of integrated packages 1 Some features that the user needs may not be available 2 Takes too much hard disk space Page 7 of 115 Www revision notes co cc What is a Custom Written Bespoke or Tailor Made Software Package 1 This is software package that has been developed to solve a specific problem of a particular organization 2 Custom written software is needed to be developed when there is no off the shelf software package available that would satisfy the needs of an organization 3 Custom written software includes all the functionalities needed to solve a specific problem but does not contain extra routines that are never used Advantages of custom written bespoke of tailor made software packages 1 The software is designed to do exactly what the user wants
66. imary _key lt LW00100 Index 200201 ENDIF 2 Since the index is the pointer containing the memory address of the page it helps the computer program to access the page directly Within the page the program accesses the record by using sequential access method What is a random access file 1 This is a file where records are written to the absolute memory or disk addresses pointed to by a set of hash keys stored in a hash table 2 A computer program can access records in a random file only directly but not sequentially How a program creates a random access file 1 When a new record is to be written to the random access file the computer program creates the corresponding hash key of the record by applying a hash function or a hashing algorithm on the primary key of the record When deriving the hash function to be applied the program takes into account the estimated number of records in the random access file 2 The program then stores the record at the memory or disk address pointed to by the hash key 3 The program stores the primary keys and the corresponding hash keys in the hash table associated with the random access file Page 41 of 115 www revision notes co cc 15 4 The hash keys are written to the hash table at sequential locations until a collision occurs 5 A collision occurs when the computer program finds two hash keys with the same value competing for the same location in the hash table
67. in a popular holiday location The first screen may ask for the general area of interest such as accommodation trips shopping entertainment etc Once the choice of accommodation has been made the next screen may offer different standards of hotels Once the choice of hotel type is made the next screen may offer different price bands Once the choice of price band is made the final screen will display the hotel or the list of hotels that matches all the requirements of the customer Graphical user interface 1 Graphical user interface GUI consists of a WIMP windows icons menus and a pointer 2 The GUI is used by selecting options from menus of choices and from a set of small pictures which represents the different options available 3 Choices are selected by using some sort of pointing device such as a mouse Example of a GUI Windows Desktop program Control Panel program of the Windows Natural language user interface The computer asks questions which elicit a response which gives the user the impression that he is talking to the computer Page 15 of 115 WwwW revision notes co cc Command line user interface Here the user communicates with the computer interactively by typing commands at a command prompt A command prompt is a character or a group of characters which the computer displays in order to let the user know that a command can be input Examples C gt or C My folder gt Characteristics of a comma
68. ine 6 EndProcedure Line 7 Function a b Line 8 Functionl a b Line 9 EndFunction Line 10 What is a statement Line 2 Procedurel x y is a statement In Line 3 Answer is one statement and Function1 x y is another statement What is an expression An expression is a line of code where two statements are combined by an equal sign For example Line 3 is an expression What is a procedure A procedure is a routine which carries out a task and may or may not return a value to the calling statement Page 5 of 115 Www revision notes co cc s RN For example the block of code from Line 5 through Line 7 is a procedure The name of the procedure is Procedure1 What is a function A function is a routine which carries out a task and always returns a value to the calling statement For example the block of code from Line 8 through Line 10 is a function The name of the function is Function What is a calling statement of a routine The statement Procedure x y in Line 2 is the calling statement for Procedure 1 The statement Function x y in Line 3 is the calling statement for Function The calling statement executes the routine procedure or function What is a parameter A parameter is a value passed to a routine procedure or function by a calling statement Examples In Line2 x and y are parameters In Line 3 x and y are parameters What is a utility program 1 U
69. ing system The system needs to have the following functionalities Page 86 of 115 WwwW revision notes co cc s6 a Add a record of a new customer to the system b Make changes in the data of an existing customer and save those changes to the system c Delete a customer s record from a system d Clear the data of a customer displayed on the user interface e Capability of browsing to the first record f Capability of browsing to the previous record g Capability of browsing to the next record h Capability of browsing to the last record i Validating the customer name by performing the character type check The Jackson structure diagram drawn to reflect the above system requirements are given below Room Booking Maintain booking Maintain checkout Search for Produce reports details details information D otes co cc Maintain customer details Input a new Edit and Delete a Clear a Move to Move to Move to the Move to customer s save an customer s customer s the first the next the last data een data data customer s previous customer s customer s customer s data customer s data data data data Cl Else C2 Else Cl Else C2 Else Condition List C1 Valid customer name C2 Valid telephone number Validate customer name Page 88 of 115 WwwW revision notes co cc Read customer name Get string of characters O O O O Set customer Set customer Set cu
70. interface What experience or knowledge the user has with data entry Under what circumstances the interface must be operated Are data to be entered time sensitive Factors that the analyst should consider when designing an HCI for information output l 2 8 9 What is the information needed to be outputted How much information is needed to be outputted What is the best way to present the information required Colors that should be used and should not be used Visual perception What are the alternative forms of output What technology is available What layout is needed The content of the information presented 10 Whether the information is for short term or long term memory Page 102 of 115 wWww revision notes co cc 2 Form Based User Interface Description of form based user interface 1 It mirrors a data capture form 2 It contains spaces to insert data 3 Drop down lists and option buttons are used to limit the choices for answers Example Interface used at the appointment counter of a doctor s office Advantages of form based user interface 1 Written instructions can be provided for the user to understand what data to enter 2 Can force the user to answer required questions and ensure that all the data is inputted 3 It makes the operator input the data in correct order 4 Easy to implement data validation rules 5 Can be used to provide restricted views for different users
71. ion 2 Workstation 7 Workstation 4 Workstation 5 Page 64 of 115 Www revision notes co cc Advantages of star topology e Ifone cable fails the other nodes are not affected e Performs consistently even when the network is being heavily used e Reliable market proven system e No problem arises with the collision of data since each computer has its own cable connecting to the server e Easy to add and remove nodes without disrupting the network Disadvantages of star topology e Costly to install because of the length of cables required e Ifthe central computer crashes the whole network goes down Ring Topology Description of the ring topology In a ring network the two ends of the bus are joined up This creates a loop so that data can be sent in both directions along the cable If there is a break in the cable the network will continue to operate because the data can go in the other direction Workstation 3 Workstation 2 Workstation 4 Workstation 7 Workstation 6 Advantages of ring topology e There is no dependence on a central computer or file server and each node controls transmission to and from itself e Can continue with a break in the network cable as the data can move in both directions along the cable e High transmission rates are possible Page 65 of 115 wWww revision notes co cc Disadvantages of ring topology e If one node of the ring breaks down transmission between any of the d
72. l requirements black box testing White box testing Implementation Plan for implementation or system changeover Acquiring the necessary hardware to implement the new system Installation of the new system Conversion of the data files Involves transcription of data from manual files to the computer or importing data from the old computer files to the new computer files Alpha testing Training the end users Beta testing Evaluation Discussion of the degree of success in meeting the original objectives Evaluate the user s response to the system Desirable extensions Page 83 of 115 WwwW revision notes co cc Maintenance Corrective maintenance Adaptive maintenance Perfective maintenance Problem definition It is important to define the problem accurately because otherwise a wrong problem may be solved It is important that the system analyst and the client must work together to define the problem accurately because 1 Client is the expert in the problem 2 System analyst is the expert with computers and technology 3 Therefore the system analyst and the client need to pool resources to come up with a clear definition 4 Also the system analyst and the client need to agree on the outcomes so that when the system is implemented there is a set of criteria to judge it Feasibility study Feasibility study means considering the problem f
73. level management information This is information such as decisions reports and responses related to the policies and objectives of the company Examples Stop producing a particular product Start producing a new product Qualifications required for the post of accountant in the organization Examples of applications for which batch processing is suitable 1 Processing payroll using hours worked data 2 Updating the customer accounts master file using the daily transaction file 3 Producing and printing monthly utility bills such as electricity bills telephone bills gas bills and water bills Examples of applications for which real time processing rapid response processing is suitable 1 Airline seat reservation system Immediately after a particular seat is booked for a particular passenger the database must be updated so that another booking agent would see that the seat is already booked This avoids double booking 2 Process control system of a food products manufacturing company The variations in temperature viscosity color pH value must be controlled immediately 3 Missile control system must launch the missile as soon as signal is inputted to the system about detecting an enemy aircraft What is an expert system Page 107 of 115 Www revision notes co cc i3 2 This is a computer program which mimics a human expert on some specialized field of knowledge Expert system also 1 Can reason with uncertain
74. lock of data is called the check sum How check sum is used to detect transmission errors 1 The check sum is calculated ignoring the carry out of the byte and is mentioned with the block of data that is being transmitted 2 The check sum is then calculated again when it is received at the receiving computer 3 The check sum calculated is then compared with the value mentioned in the block of data 4 If the two values match there has been no error in transmission If they do not match there has been an error in transmission Page 68 of 115 WwwW revision notes co cc What is parity 1 The sum of all the 1 bits in a byte of data is called the parity Parity can be either odd or even 2 The parity of each byte of data must be equal to the parity defined for that computer 3 If the parity of a byte of particular piece of data is different from the parity of the computer then the parity bit of the byte is changed so that the parity of the data will match the parity of the computer How parity check is used to detect data transmission errors 1 The parity of each byte of data that reaches the receiving computer is checked against the parity of the sending computer 2 If the two parities match there has been no error in transmission If they do not match there has been an error in transmission What is circuit switching Circuit switching has a fixed path through the network between the sending computer and the destination co
75. mputer is opened and held for the entire time duration of data transmission What are the advantages of circuit switching The message arrives at the receiving computer without having its data to be reordered What is packet switching 1 The message is split into a number of equal sized packets 2 Each packet is labeled with the destination address and the packet number 3 Packet switching transmits individual data packets into the network to find their way to the destination computer independently of each other 4 At each node the label is checked and the packet is redirected 5 At the destination computer the packets are reordered and reassembled according to their packet numbers Destination computer Sending computer Page 69 of 115 wWww revision notes co cc 10 What are the advantages of packet switching 1 Large part of the network is not tied up for long periods of time 2 Message is difficult to be hacked What are the disadvantages of packet switching 1 Transmits at the speed of the slowest packet 2 Packets must be reordered and reassembled at the destination What is a protocol A protocol is a set of rules which control the data transmission in a network What are the features or rules of protocols 1 Type of data transmission or whether the data transmission is serial or parallel Errors would occur if one device has a serial connection and the other device expects a parallel con
76. nd line user interface 1 The user needs to know what commands are available 2 The user needs to understand the commands 3 The user needs to understand the way that the data and files are stored in the computer system 4 Used in systems which are much more open than the other types of systems where the user is restricted to the options available to him 5 Command based interfaces can only be used by computer literate people Page 16 of 115 wWww revision notes co cc Chapter 1 3 Programming Tools and Techniques Structure of a Computer Program A program is a set of instructions written in a programming language to solve a problem The processor of the computer reads these instructions and executes them to perform the tasks necessary to solve the problem The Lifetime of a Computer Program There are three stages in the lifetime of a computer program 1 Design time This is the time spent by the programmer in coding and testing the computer program The length of this time depends on how long and complex the program going to be It can be few days or even several months 2 Compile time This is the time that the compiler spends in compiling the source code This is a relatively short time period A simple program may take only a second to get compiled A long and complex program might take even few minutes to get compiled 3 Runtime This is the time that the program is getting executed It is during the runtime that the
77. ndexes also increase This makes it necessary to divide the index also into pages An index which itself is divided into pages is called a multi level index Index File Page 1 Primary Key Index LW00001 20001 Memory Primary Key Student Telephone Address LW00002 20001 Address Name LW00003 20001 20001 LW00001 John 0112398752 Colombo LW00125 20101 20100 LW00100 Peter 0112764900 Jaffna LW00126 20101 LW00127 20101 LW00257 20201 LW00258 20201 LW00259 20201 Page 2 Memory Key Student Telephone Address Address Name 20101 LW00101 Brian 0112367489 Kalutara 20200 LW00200 Lisa 0114872901 Negambo Page 3 Memory Key Student Telephone Address Address Name 20201 LW00201 Wendy 0112897236 Colombo 20300 LW00300 Colin 0115278340 Kandy Page 40 of 115 WwwW revision notes co cc 14 How a program access records in an indexed sequential file 1 When the user enters the primary key of the record which he wants to access the program uses the index file to find the index of that primary key When the above sample file is considered the program uses the following algorithm to find the index IF primary_key gt LW00001 and primary _key lt LW00100 Index 200001 IF primary_key gt LW00001 and primary _key lt LW00100 Index 200101 IF primary_key gt LW00001 and pr
78. nection 2 Mode of data transmission or whether the data transmission is full duplex half duplex or simplex 3 Bit rate since both devices must talk and listen at the same number of bits per second Otherwise bits may be missed or counted twice 4 Error checking whether the parity is odd or even whether echoing back is used whether check sums are used Why a protocol should be arranged in a layered fashion Individual layers of protocol can be altered without altering the other layers when hardware and software are changed Page 70 of 115 Www revision notes co cc Chapter 1 6 Data Transmission and Networking A network is a collection of computers printers scanners routers bridges switches and other devices which are connected to each other by some transmission medium The devices connected in the network are called nodes of the network Network transmission media A network transmission medium is the medium through which the data flow from one node to another in a network Network transmission media are of two types 7 Cable media such as metal cables and fiber optic cables Metal cables used as network transmission media are coaxial cables unshielded twisted pair UTP cables shielded twisted pair STP cables and fiber optic cables Wireless media such as radio waves microwaves infra red waves LANs and WANs Networks are divided into two types based on the extent of geographical ar
79. ned What is meant by network topology The physical layout of network nodes is called the network topology What are the widely used network topologies Bus topology star topology and Ring topology Bus Topology Description of the bus topology All the devices on the network share a single cable known as the bus cable Each node is independently attached to the common bus cable Data can be transferred from any computer to any other computer The bus cable ends at a terminator which absorbs electrical signals so they don t bounce or reflect back and forth on the bus The bus cable is located inside a hub and each piece of cable connected to the bus cable has its other end connected to a port on the hub Page 63 of 115 Www revision notes co cc Workstation 1 Workstation 2 O I I LJ LJ Terminator Bus Cable Port on Hub Terminator Hub Advantages of bus topology e Easy and inexpensive to set up as it requires the least amount of cables compared to other topologies e Easy to add nodes without disrupting the network Disadvantages of bus topology e The whole network goes down if the main bus cable fails at any point e Cable failure is difficult to isolate e Network performance degrades as the number of computers increase Star Topology Description of the star topology In star topology each node is connected to a central computer which controls the network Central Computer Workstat
80. nsure that the correct hardware is available 2 Must train the staff to use the new system 3 Must input the data to the data files either manually or by importing them from the original System Page 93 of 115 WwwW revision notes co cc 213 Following are the four system implementation changeover methods 1 Parallel running The old and new systems are run side by side until it is made sure that the new system is fault free This method of implementation is adopted where a system failure is not affordable The advantages of this method are that a The results of the two systems can be compared to ensure that there is no fault with the new system b The staff training on the new system can be carried out effectively c Always have a fall back system in case of a system failure The disadvantage of this method is that it is very expensive as the things have to be done twice Examples of systems which are ideal for implementing with parallel running are Exam marks processing system Examples of applications for which parallel running is not suitable are control system such as traffic light systems and process control systems 2 Pilot running The new system is implemented initially only in a certain part of the company such as a branch The advantages of this method are that a If there is a fault in the new system it would affect the organization only in a relatively small area of data processing b It allows the
81. olerances in the transmission as the bits can become muddled up Examples of different types of data transmission 7 The data transmission in a network using cables is serial 7 The Data transmission inside the computer using the bus system is parallel This is because of the very high speed of data transmission needed by the computer s processor in order to process them For example the data transmission between the primary memory and the hard drive of the computer is parallel because the processor requires the data to be downloaded to the memory as quickly as possible The data transmission between the computer and the printer is parallel because the computer needs to send a big chunk of data to the printer s buffer quickly so that the processor will be free to attend to other tasks of the computer Modes of data transmission Data transmission can be divided into the following three modes Duplex mode Half duplex mode Simplex mode Duplex mode of data transmission means passing data in both directions at the same time between two devices Page 76 of 115 wWww revision notes co cc RN Half duplex mode of data transmission means passing data in both directions between two devices but only in one direction at a time Simplex mode of data transmission means passing data only in one direction between two devices Examples of different modes of data transmission 2 The data transmission between the
82. olution violate law If the solution violate any laws of the country it is not feasible 9 Will the solution take a long time to develop If the solution takes too long to develop the company may go out of business Information requirements of the system and fact finding It is extremely important that the analyst finds out all the information about the requirements of the system Following are the methods of fact finding 1 Interviewing key personnel Advantage of this method are that it allow a Questions to alter according to the answers given b Employees to reveal confidential information 2 Questionnaires Advantage of this method are that it allow a A large number of people to give their views in a very short time period b Maintain the anonymity 3 Meetings Advantage of this method is that it allows a Discussion between people at the meeting 4 Inspecting documents Advantage of this method is that it allows a Obtaining the format of input and output 5 Observing the business operations Advantage of this method is that it allows a Obtaining first hand information of what actually happens in the system Requirement specifications 1 Preparation of the list of tasks to be performed in system development arranged in the order of priority This list of tasks is the basis for the system design Page 85 of 115 Www revision notes co cc 2 Determination of the requirement specifications for data a Ty
83. omputers 1 Employees can work faster 2 Messages can be sent faster to coworkers and customers through email 3 Can keep the working environment neat and clean 4 Can work from home 5 Can search and find information quickly by using computerized dictionaries and encyclopedia 6 Can transfer files easily to other employees 7 Get more leisure time 8 New jobs are created which helps the employee in advancing his career State the disadvantages gained by the employees of a company by using computers 1 Less social interaction with the coworkers 2 Health is affected 3 Confidential data getting hacked 4 Getting addicted to computer games 5 Inability to work when the electricity is gone 6 Need to get skills and training in new technology 7 Some employees who are not skilled in technology might lose their jobs State the advantages gained by the management of a company by using computers 1 Can get done the work faster and thereby attract a bigger customer base 2 Can occupy a smaller office as the file storage space is reduced 3 Can make the staff work at home thereby reducing the expenses on s electricity 4 Can use new technologies to cut down on labor cost such as robots Page 109 of 115 Www revision notes co cc State the disadvantages gained by the management of a company by using computers l 2 3 Has to invest a big amount of money in hardware and software Has to spend money to maintain the software
84. on with classmates and friends 2 Allows access to a large amount of educational material 3 Allows students to learn at their own speed 4 Allows students to learn at own times What are the disadvantages of having unrestricted access for the students to the Internet 1 Many sites give inaccurate information 2 Many sites contain inappropriate material such as pornography 3 Many sites encourage breaking laws 4 Sites available to buy coursework 5 Sites available that teaches how to cheat at exams 6 Allows hackers enter the system 7 Allows downloading viruses What are the benefits to the worker in working from home 1 Quality of life improves 2 Can work around other commitments 3 More time can be spent with family What are the disadvantages to the worker in working from home Page 112 of 115 Www revision notes co cc 1 Loses social interaction 2 Distractions from family members such as children 3 May need training in the use of technology What are the benefits to the businesses due the workers working from home 1 No need of large and expensive office space 2 Will have lower utility bills such as gas water and electricity 3 Can have a happy work force 4 Can have world wide workforce What are the disadvantages to the businesses due to the workers working from home 1 Greater security issues relating to the data and information 2 Difficult to monitor what workers are doing 3 Difficult to make
85. or how to perform a certain data processing task 2 Software makes the computer system produce useful results What is live ware Live ware is people involved in developing and implementing an information system Examples system analysts software engineers network administrators etc How software is classified Software System Software Application Software a E Operating Translator Utility Libraries Systems Programs Programs Generic General Purpose Packages Word Processors Spreadsheets Databases Compilers Presentation Graphics Desktop Publishing Interpreters Web Browser Email Assemblers Computer Aided Design Web Publishing Graphic Design Project Management Disk formatter File handler Integrated Packages Hardware or device driver File compressor Custom Written Bespoke or Tailor Made Packages Virus checker Off The Shelf Packages Software Development Packages Visual Basic Java C What is a package A package is a software program which is bundled with a user manual Why does a computer system need to have input devices To enter data to a computer system Page 2 of 115 www revision notes co cc Why does a computer system need to have output devices To present the results produced by the computer system to the user Why does a computer system need to have secondary storage devices backing stores 1 To store files when the power to the processor is turned off 2 To store data
86. pe of data This helps to determine the form that the data will be stored whether ASCH JPEG etc and the amount of storage space required for each set of information b Data structures to be used Whether arrays linked lists stacks queues or binary trees are required to organize and handle data depending on the situation to be handle c Data access methods Whether the data are supposed to be accessed individually one at a time or they all are supposed to be accessed in one run d Whether the data is static do not change frequently or change frequently Determination of the requirement specifications for input a Nature of the data to be inputted i e whether graphical textual or physical b Is the data already in existence or whether they have to be collected c The skill level of the data entry operator d Design of the user interface Determination of the requirement specifications for output a Nature of the information to be outputted whether on screen printed sound light or mechanical b Color codes to be used for on screen output c Dialog boxes used to display error messages and alerts d Specific type of printer to be used in the case of printed output Jackson structure diagram The solution is gradually divided into modules which are more manageable Jackson structure diagram is the representation of these modules in a hierarchical diagram Example A hotel needs to computerize its room book
87. peakers 6 Projector Page 59 of 115 wWww revision notes co cc 12 Page 60 of 115 www revision notes co cc Chapter 1 6 Data Transmission and Networking What is a network A network is a collection of computers printers scanners routers bridges switches and other devices which are connected to each other by some transmission medium The devices connected in the network are called nodes of the network What is a network transmission medium Network transmission medium is the medium through which the data flow from one node to another in a network What are the types of network transmission media Network transmission media are of two types e Cable media metal cables fiber optic cables e Wireless media radio waves microwaves infra red waves What metal cables are used as network transmission media Coaxial Cables Unshielded Twisted Pair UTP cables Shielded Twisted Pair STP Cables Fiber Optic Cables What is a local area network LAN A LAN is a network of computers in a small geographical area such as a school a company an office or a factory What is a wide area network WAN A WAN is a network of computers in a large geographical area such as several cities or even countries The largest WAN is the Internet which is global How LANs differ from WANs LAN WAN LAN exists in a small geographical area WAN exists in a wider geographical area Page 61 of 115
88. peed mismatch e This is done by collecting and preparing the data during a defined time period and bundling them into one batch The whole batch will then be processed by the processor where the user does not have to be involved What are the instances where batch processing is sensible 1 When there is a large amount of data to be processed 2 When data collected is very similar 3 When data requires very similar processing 4 When processing cannot be started until all the data is collected 5 When no human intervention is necessary once the processing starts 6 When the computer has identifiable times where it is not being used and so has available processor time What are examples of batch processing 1 Producing bank statements from customer s account details 2 Producing utility bills gas electricity and telephone bills from customer records 3 Producing payroll of an organization from hours worked and pay rates 4 Compilation of high level language programs where a number of users want programs Compiled What is real time processing Data input is processed fast enough to effect the next input What are examples of real time processing 1 Controlling the temperature of a reaction vessel where the processor accepts temperature data inputted from a sensor and then makes a decision whether to adjust the heating elements of the vessel 2 Controlling a robot trolley by a processor which accepts input from a sen
89. plications For example a video file that has been compressed may require expensive hardware to decompress it so that it is fast enough to be viewed Error checking and correcting in data transmission When data is transmitted in a network the bit stream can get affected due to various reasons which makes the data at the receiving computer to contain errors The methods that can be used for checking transmission errors are gt Echoing back gt Check sum gt Parity Echoing Back The receiving computer sending back the data to the sending computer is known as echoing back The data echoed back is checked against the data that was sent in the first place by the sending computer If they match there has been no error in transmission If they do not match there has been an error in transmission and the data will be sent again Page 80 of 115 WwwW revision notes co cc RN The disadvantages in echoing back are that it takes a long time to transmit data as the data has to be sent twice and it can be implemented only in duplex or half duplex modes Check sum Check sum is the sum of all the bytes in a block of data gt Check sum is used by the computer to detect transmission errors as described below gt The check sum is calculated by the sending computer ignoring the carry out of the byte and is mentioned with the block of data that is being transmitted gt The check sum is then calculated again when it is received at the recei
90. positing process of money Example 3 Computerized ticketing machine system 1 One phase can be the issuing of the printed ticket and returning the balance money only when the coins are put into a till 2 Another phase can be the capability of using a magnetic swipe card or smart card to pay the bus fare Example 4 Point of sale system 1 One phase can be the capability of using the barcode scanner as the device to input the product ID 2 Another phase can be the capability of using magnetic swipe card or smart card facility to pay the bill by a credit card or a debit card Example 5 Pay phone system 1 One phase can be the capability of taking a call by inserting coins or bills to the system 2 Another phase can be the capability of using a prepaid phone card to pay and take the call Example 6 Proximity card system 1 One phase can be where the data entry to the system is done by using a concept keyboard i e the user types in the pin number using the keyboard of the machine Page 95 of 115 www revision notes co cc i RN 2 Second phase can be where the data entry to the system is done by swiping a magnetic card 3 Third phase can be where the system uses a finger print scanner for data entry 4 Direct Conversion or big bang The new system replaces the old system immediately and completely The advantages are that a The cost of implementation is less b No confusion to the staff The disadvantage is that it is
91. presented by 1 s and 0 s A language which contains only binary code is called a machine language Machine language code is very hard for a programmer to understand Therefore programmers use high level programming languages to write programs A program written by a programmer in a high level language is called source code Source code code written in high level language is more English like and can be understood easily by a programmer The process of converting source code a program written in a high level language to machine language is called program translation Program that performs translation is called the translator When source code file is translated the code produced is also called object code The object code is normally much bigger than the source code because it needs several machine language instructions to represent one high level language instruction There are three types of translators e Compilers e Interpreters e Assemblers Types of Programming Errors 1 Syntax Errors The errors made by violating the rules of a programming language are called syntax errors The correct spelling of a code may be PRINT If the code is written by the programmer as PLINT the translator program would not recognize it and so would not be able to translate it A compiler detects syntax errors and highlights the error in the source code usually by displaying an error message to alert the programmer The program does not get
92. pseudo code and or program flowcharts b Programming language used c Data structures used d Library routines and components used Technical documentation This documentation describes anything that will be helpful for a technician to maintain the system Therefore it is also known as the system maintenance document Technical documentation contains a System design specifications and b Program specifications Page 92 of 115 WwwW revision notes co cc 12 5 User documentation This documentation describes the things that would be helpful for a person who will be using or operating the system Why technical documentation is necessary Because a technician can alter the system or correct the system when necessary Why user documentation is necessary It provides instructions for users about how to use the system and what to do when something goes wrong What are the items to be included in the user manual 1 Details of how to enter data 2 Details of how to use the system illustrated with screen shots 3 Help facilities and frequently asked questions 4 Troubleshooting guide for errors What are the items to be included in the technical manual 1 Details of installation and start up procedure 2 Minimum system specifications of the computer on which the software is to run 3 Algorithms 4 Database design Testing and implementation planning When implementing the new system the analyst 1 Must e
93. r s processor It consists of RAM random access memory ROM read only memory cache memory and registers Page 49 of 115 WwwW revision notes co cc 2 What is secondary storage or backing storage This is the storage where the data is stored for future use and cannot be accessed by the processor directly Differences between RAM and ROM RAM ROM 1 Data in RAM can be easily changed 2 Data in ROM cannot be changed 2 RAM is volatile contents in the RAM 4 ROM is non volatile contents in the ROM disappears when power is turned off does not disappear when power is turned off 3 RAM stores the operating system application 4 ROM stores special programs such as the programs that are currently running in the bootstrap program that is used to load the computer and the data that is being used operating system 4 RAM is usually larger than ROM 3 ROM is usually small Similarities between RAM and ROM 1 Data stored in both RAM and ROM can be can be accessed by the CPU directly 2 Data stored in both RAM and ROM can be accessed by the CPU randomly in any order Differences between the primary storage and the secondary storage 1 Data in the primary storage can be accessed directly by the processor whereas the data in the secondary storage cannot be accessed directly by the processor 2 Data from the primary storage can be read faster than from the secondary storage This is due to the reason
94. risky If the new system has a fault and malfunctions there will be a loss of data and even the loss of customers Allows no time for training and finding errors in the system Explain what implementation method is suitable for a new POS system developed for a supermarket Parallel running is not feasible as customers would not put up with the delays Pilot running can be done by implementing the new system only in some of the checkout counters It would cause no problems even if it fails because the customers can be moved to other counters which run the old system Also it is ideal for training the cashiers to the new system Direct conversion is risky because if the new system fails all the counters have to be closed which means that the store must be shut down System maintenance and the software lifespan The three kinds of system maintenance and the reasons for the system maintenance are 1 Corrective maintenance Page 96 of 115 wWww revision notes co cc i RN This kind of maintenance is performed to correct bugs found in the system after the system has been commissioned 2 Adaptive maintenance This kind of maintenance is performed to make changes in the system because of the changes that have taken place in way that the organization works for example due to the changes in tax rates due to the changes in law etc 3 Perfective maintenance This kind of maintenance is performed to improve the performance of the system
95. rom 0 When an array is initialized it has a fixed size in memory Therefore it is not possible for a program to increase the number of data items more than the size declared for the array Linked List Record 1 Record 2 Record 3 gt Null Record 4 1 A linked list is a data structure which is a list where the nodes may not be next to each other in the computer s memory 2 Each node contains a data item or a record and a pointer which carries the address of the next node in the list 3 Start pointer references to the first node of the linked list 4 Nextfree pointer points to the next free location of the free list 5 The last node contains a Null pointer to indicate that there are no further items Page 33 of 115 wWww revision notes co cc A STe Algorithms involving Linked Lists lgorithm 1 Insertion of a data item to a sorted linked list Before the data was inserted NTR ee ee After the data was inserted START Bob First data Previous data Current data Next gt David J gt Edward LINKED LIST New data IF free list is empty THEN OUTPUT error message ELSE store the new data in the node pointed to by the NEXTFREE pointer READ data from the linked list following the pointers IF new data lt current data IF current data lt gt first data change the pointer of the previous data to point to the new data ch
96. rom the point of computerization and making a report to the organization saying whether a computerized solution is possible and sensible Feasibility study will consider the problem and the proposed solution from the following points of view 1 Is the solution technically possible If the hardware equipment and or software tools do not exist to carry out the tasks then it doesn t matter how good it would be it cannot happen 2 Is the solution economical to produce If the cost of the computerized solution is so great that the company cannot recover the cost then the solution is not feasible 3 Is the solution economic to run If the cost of running the new solution is higher than the current system then the solution is not feasible 4 Are there any social implications If the human cost due to mass redundancy due to the introduction of the computerized solution is very high the solution may not be considered as feasible 5 Is the workforce skilled enough If there are no skilled people to operate the equipment and the software the solution will not be Page 84 of 115 wWww revision notes co cc feasible 6 Will the customer notice a difference If the customer sees no difference in the price quality and reliability in new solution and not get impressed then the solution will not be feasible 7 Will the profits increase If the profit won t increase due to the new solution it would not be feasible 8 Will the s
97. senting an algorithm are 1 Pseudo code 2 Program flowchart Example 1 Write an algorithm to calculate and display the sum of all even numbers and the sum of all odd numbers less than 20 START TotalOfEvenNumbers 0 TotalOfEvenNumbers 0 Counter 1 Read Number WHILE Counter lt 20 Read next number IF Number Mod 2 0 THEN TotalOfEvenNumbers TotalOfEvenNumbers Number ELSE TotalOfOddNumbers TotalOfOddNumbers Number ENDIF Counter Counter 1 ENDWHILE DISPLAY TotalOfEvenNumbers DISPLAY TotalOfOddNumbers END Page 25 of 115 WwwW revision notes co cc 10 Example 2 Write an algorithm to calculate and display the square numbers between 1 and 20 N 1 WHILE S lt 100 S N N N N 1 Display S ENDWHILE Example of an algorithm Algorithm to turn on a cooling fan only when a motion sensor detects that there is a person in the room M 1 and the temperature in the room T measured by a thermistor is above a set value D START WHILE system is ON WHILE M Not Triggered IF Fan is On THEN Fan Off ENDIF ENDWHILE IF T gt D THEN IF Fan is Off THEN Fan On ENDIF ELSE IF Fan is On THEN Fan Off ENDIF ENDIF ENDWHILE END The same algorithm can also be written as given below START WHILE system is Triggered on READ M REPEAT IF T gt D AND Fan off THEN Fan On ELSEIF T lt D AND Fan On THEN Fan Off ENDIF Www r
98. sferred to countries outside the European Economic Commission without adequate protection Mention the measures included in the Data Protection Act of 1998 to keep personal data confidential l 2 Make sure that the data is obtained lawfully Provides the right to see the data held to ensure that it is correct 3 Allows checking whether the data held is relevant to the purpose 4 Sa Ensures that out of date information is destroyed Limits personnel who are able to see the data Implications on employees of using an expert system Page 114 of 115 Www revision notes co cc l 2 3 Employees need not be trained Employees may not be able to learn new skills Employees may lose skills because of the reliance on the system Implications of computer use by the staff at a computerized manufacturing company 1 2 Some jobs will be lost More jobs will be created in some areas Demands more training programs Older workers may not be able to retrain Training leads to extra qualifications Training leads to extra responsibilities More highly paid jobs will be available Deskilling Health and safety issues Page 115 of 115 Www revision notes co cc
99. sor while following a black line on the floor and makes a decision concerning steering to keep the trolley on the line 3 A catalog shop processing orders using the code of a product inputted by the operator and the system then comparing the code with the data containing in the files If the product is found Page 12 of 115 Www revision notes co cc a RN and the customer wants to buy the product it is required to record the fact that the item has been sold Otherwise a second person might be sold the same item Characteristics of a real time computer system In real time processing since the data must be processed immediately the operating system needs to be ready to handle input as soon as it comes in This means that the real time computer system cannot be used to do other tasks during some of its slack times This means that the computer will not be using its full potential as far as processing is concerned In other words the computer system engaged in real time processing tends to display a high degree of redundancy What is on line processing This is processing of data while communicating with the processor directly An example for on line processing is updating a bank s customer accounts master file with the daily transaction file at the end of the business day What is off line processing Processing of data without connecting to the processor An example for off line processing is filling up an order form downloa
100. stomer Set customer name to invalid name to invalid name to invalid name to invalid Condition List C1 Until number of characters 1 C2 ASCII value is between 0 and 31 C3 ASCII value is between 33 and 64 C4 ASCII value is between 91 and 96 C5 ASCII value is between 123 and 127 6 Data flow diagram Data flow diagrams are used to model an information system in terms of the data data flows processes and data stores It also shows the entities from where the data originate and to where the data flows in Page 89 of 115 wWww revision notes co cc The following symbols are usually used when drawing the data flow diagrams External Entity Calculate Process dsconnt D1 Customers Table Data store p Data flow 7 System flowchart This is the diagram which shows the sequence of the business operations of an information system The following symbols are used when drawing system flowcharts Manual input example keyboard Process Decision Visual display unit Magnetic disk Magnetic tape POTOUL Page 90 of 115 Www revision notes co cc 10 Document or printout C Computer data file O Sort data Manual operation done by hand such as operating the OMR C Page connector System evaluation against the initial specifications 1 Why evaluating the new solution against the initial specifications is important to the end user
101. t commonly used protocol stack in data transmission It is the protocol stack used in data transmission in the Internet too HTTP and FTP are commonly used protocols which operate in the application layer of the OSI reference model HTTP is used in the transmission of Web pages and FTP is used in the transmission of files Application layer Sending Receiving Application layer i computer computer E l rotocol layers to the layers to the 2 transmission transmission the top to the the bottom to bottom of the the top of the stack stack Sending Computer Receiving Network Transmission Medium Computer Protocols are arranged in a layered manner because individual layers of protocol can be altered without altering the other layers when hardware and software are changed Importance of bit rate in data communication Number of bits that can be transmitted in a network in one second is known as bit rate The unit used to measure the bit rate is Baud 1 Baud 1 bit per second Bit rate is an important aspect of data communication because the bit rate of the sending device and the bit rate of the receiving device must be the same for data communication to be taken place properly Bit rate also enables the following 7 Standardization of the methods of data communication One layer of the protocol to be altered without altering the entire protocol Page 79 of 115 Www revision notes co cc 7 Manufacturers to design h
102. te is an important part of communication This is because it enables 1 Standardization 2 One layer of the protocol to be altered without altering the entire protocol 3 Manufacturers to design hardware and software for a particular layer Page 67 of 115 Www revision notes co cc s RN Why bit rate is an important part of any protocol Because if one device sends data at a particular bit rate and the other device reads what it receives at a different rate the message would never be received correctly Error checking and correcting When data is transmitted in a network the bit stream can get affected due to various reasons which makes the data at the receiving computer to contain errors The methods that can be used for checking transmission errors are 1 Echoing back 2 Check sum 3 Parity What is echoing back The receiving computer sending back the data to the sending computer is known as echoing back How echoing back is used to detect transmission errors The data echoed back is checked against the data that was sent in the first place by the sending computer If they match there has been no error in transmission If they do not match there has been an error in transmission and the data will be sent again Disadvantages of echoing back Takes a long time to transmit data as the data has to be sent twice Can be implemented only in duplex or half duplex modes What is check sum The sum of all the bytes in a b
103. th greater positional accuracy A light pen can work with any CRT based monitor but not with LCD screens projectors and other display devices Used in CAD systems 7 Joystick A stick when moved which makes the cursor move in the same direction 8 Scanner Used to scan text or pictures into the computer s memory 9 OCR 1 Optical Character Reader 2 Used to scan documents such as data capture forms where it reads translates converts the printed and handwritten characters into computer characters and transfer those characters to the computer 3 Light reflected off characters determines the shape of characters 4 OCR uses a template of characters stored in it to compare with the characters in the source document in order to recognize them 10 OMR 1 Optical Mark Reader 2 Used to scan paper documents containing marks at specified locations and to recognize them 3 OMR uses a template document containing the marks at correct locations to compare with the marks in the source document in order to recognize the correct answers How the form and its contents can be affected by the need to use OMR 1 The form used to mark data must have areas at identified locations to shade or mark 2 Printing in the sensitive areas of the sheet is done using a special type of ink in a light color such as light blue or pink which the OMR does not see 3 Form should only be used in one side Page 56 of 115 WwwW revision notes co c
104. these types of keyboards may include elevated sections at various angles This keyboard has its keys arranged in curves so that the palm of the hand can be supported on the keyboard comfortably while typing What is ergonomics Ergonomics is the science of adapting products and processes to human characteristics and capabilities in order to improve people s well being and optimize productivity Ergonomics ensure that products and environments are comfortable safe and efficient 2 Mouse A pointing device used to translate its movements on the desktop into digital information this is fed to the computer which in turn causes the cursor to move on the screen There are mechanical mice and optical mice Mouse has two or three buttons used to make selections on the screens 3 Tracker ball A pointing device used in laptop computers 4 Touch sensitive pad track pad Used in notebook computers Operate by moving a stylus or a finger across a pad which moves the cursor on the screen 5 Touch screen A screen sensitive to touch Used to select an item from a menu Used in banks and restaurants Input device useful for users who are not computer literate RN Page 55 of 115 Www revision notes co cc a RN 6 Light pen A light pen is a light sensitive wand used in conjunction with the computer s CRT monitor It allows the user to point to displayed objects or draw on the screen in a similar way to a touch screen but wi
105. tility programs are routines added to the operating system to carry out common tasks in the computer system 2 Examples for utility programs are Disk formatter File handler Hardware or device driver File compressor Virus checker What is a component A component is a compiled routine or a set of compiled routines which carries out a specific task or a set of tasks and which does not have a user interface What is library 1 A library is a collection of components 2 A library is different from an executable because it cannot run as an independent program 3 A Library gets linked to an executable at compile time or runtime to provide the executable some specific service in data processing Page 6 of 115 Www revision notes co cc What is DLL A library that links to an executable in runtime is called a dynamically linked library DLL In contrast a library that links to an executable in compile time is called a statically linked library What is generic or general purpose software 1 Generic software is software which is appropriate to many applications within a skill area 2 Examples of generic software are Word Processors Spreadsheets Database Management systems Presentation Graphics Desktop Publishing Web Browser Email Computer Aided Design Web Publishing Graphic Design Project Management What is an Integrated Software Package This is a software package built by combining parts from several appl
106. tion in a popular holiday location The first screen may ask for the general area of interest such as accommodation trips shopping entertainment etc Once the choice of accommodation has been made the next screen may offer different standards of hotels Once the choice of hotel type is made the next screen may offer different price bands Once the choice of price band is made the final screen will display the hotel or the list of hotels that matches all the requirements of the customer Command Line User Interface Description of command line user interface 1 User types in a command at a command prompt which appears on the screen A command prompt is a character or a group of characters which the computer displays in order to let the user know that a command can be input Examples C gt C My folder gt 2 User must ensure that the syntax is correct 3 User must learn the commands 4 The interface allows access to the whole system Example Interface used by a system administrator looking after a network Advantages of command line user interface 1 Fast to operate as it is done through the keyboard Page 104 of 115 wWww revision notes co cc 2 Can access the whole system Disadvantages of command line user interface 1 The user needs to understand the way that the data and files are stored in the computer system 2 Difficult to understand and learn the commands 3 Difficult memorize the commands 4 Can only be us
107. to a format that the processors of the communicating computers can understand Hardware and software needed for communication in a WAN gt gt gt Network interface card which is used to connect computers by cables Modem ISDN or ADSL adapter which is needed to access the telephone system Dial up software which is needed to connect to a Web server or to access the telephone lines Advantages of using a network of computers over using a collection of stand alone computers Allows sharing of hardware such as disk storage printers image scanners modems and central servers Allows sharing of data and information held in one computer among the users of the network where their computers are connected Allows sharing of application programs held in one computer and make them available to all users rather than having copies installed on each computer Allows sharing of a file server where all the users can save their files and have that one computer backed up instead of backing up all the computers It allows sharing of a centralized database It allows electronic mail and messages to be sent between users It allows the implementation of centralized security for computer files Allows having one proxy server to have the Internet connection and have the users of all the other computers in the network log in to the proxy server to access the Internet It allows different types of computers to communicate with each other Page 72 of 1
108. ue or values passed to the procedure or the function in the calling statement is called parameters An example of using a procedure Calling statement Parameters Ca CalculateAverage ComputingMarks PhysicsMarks AccountsMarks Private Sub CalculateAverage ComputingMarks PhysicsMarks AccountsMarks Average ComputingMarks PhysicsMarks AccountsMarks 3 IblAverage Average End Function An example of using a function Calling statement with parameters IblAverage CalculateAverage ComputingMarks PhysicsMarks AccountsMarks Private Function CalculateAverage ComputingMarks PhysicsMarks AccountsMarks Average ComputingMarks PhysicsMarks AccountsMarks 3 CalculateAverage Average End Function Page 19 of 115 WwwW revision notes co cc a RN Modularizing a Program and Top Down Design The process of dividing a program gradually into parts and those parts into further subparts until where each subpart can perform a specific manageable task is called modularizing the program Each subpart is called a module Designing programs in this manner is called top down design Consider that it is necessary to develop a program to solve the problem of computerizing the traffic lights in the middle of a city The solution is a very complex one but it can be split into the following parts 1 How is the data going to be collected from sensors and stored in the system 2 How is the decision going to be made abo
109. ue Gua Queue is a list of items where i Front TP HP Page 35 of 115 WwwW revision notes co cc o RN e Insertions are made to the rear of the queue and deletions are made from the front of the queue e First item in becomes the first item to be out FIFO A queue needs two pointers because adding data to the queue is done at the rear of the queue and deleting an item from the queue is done at the front of the queue The Head Pointer HP points to the front of the queue and the Tail Pointer TP points to the rear of the queue Algorithms involving Stacks and Queues A problem that can occur when a program tries to insert a new value to a stack or a queue which is represented as an array is encountering the situation where the array is full The stack pointer helps to recognize this situation by pointing to the outside of the array A problem that can occur when a program tries to read a value from a stack or a queue which is represented as an array is encountering the situation where the array is empty The stack pointer helps to recognize this situation by pointing to the null value Algorithm 4 Insertion of an item to a stack when the stack is represented by an array j Memory addresses increase in this direction Stack Pointer points to the top of the stack IF stack is full DISPLAY message Stack is full STOP ELSE Increment stack pointer by 1 Store the new data at the location pointed to by the stack pointer
110. ut the changing of the lights 3 How is the data collected from the pedestrian crossing and then stored 4 How is the data processed 5 What outputs are necessary and how they are presented Each of these solutions performs a specific task and is more manageable than the overall problem and is called a module Therefore the program to solve the overall problem of developing a solution for the traffic lights system can be coded as a set of separate modules Advantages of Designing a Program in Modular Form 1 Fewer errors are made when coding because code containing in each module is shorter 2 Algorithm in a module can be easily understood 3 A team of programmers can be used where each one would code one module It will reduce the overall development time of the solution 4 Programmers can be assigned modules to be coded based on their individual expertise 5 Each module can be tested thoroughly 6 Allows library programs to be inserted easily Disadvantages of Designing a Program in Modular Form 1 Can lead to problems when naming variables 2 Can lead to problems when modules are linked because links must be thoroughly tested 3 Documentation of modules will become tedious Bottom up Programming Building a program by writing code to use a set of components is called bottom up programming Page 20 of 115 WwwW revision notes co cc Program Translation Computer s processor can understand only the binary code which is re
111. ving computer gt The check sum calculated at the receiving computer is then compared with the value mentioned with the block of data gt Ifthe two values match there has been no error in transmission If they do not match there has been an error in transmission Parity check Parity is the sum of all the 1 bits in a byte of data Parity can be either odd or even The parity of each byte of data must be equal to the parity defined for that computer If the parity of a byte is different from the parity of the computer then the parity bit of that byte should be changed to match the parity of the computer before that byte is transmitted out of the sending computer Parity check is used by the receiving computer to detect data transmission errors in the following manner The parity of each byte of data that reaches the receiving computer is checked against the parity of the sending computer If the two parities do not match the receiving computer reports that an error has occurred while the data is in transit If the two parities match an error may or may not have occurred and the receiving computer is unable to report whether an error has occurred This is because the parities would match even if a double error occurred where two bits may have changed Example Suppose that the parity of the sending computer is even The bit pattern of the byte 1001011 can change to 1101111 while the data is in transit Here both the second and fifth bits h
112. when they have to be used again later 3 To store files which are too large to be stored in the main memory 4 To allow for the transfer of data from one computer system to another What is system software System software controls how the computer system works What is application software Application software allows the user to make the computer do something useful What is operating system 1 Operating system is a software program which controls the operations of the computer system 2 It provides a user interface 3 It controls how the computer responds to user s requests 4 It controls how the hardware communicate with each other 5 It provides an environment in which application software can be executed What is source code Source code is the code written by a computer programmer in a high level programming language What is machine language This is the code that can be understood by the computer s processor It contains only 1 s and 0 s What is translator program 1 Translator program converts source code written in a high level programming language to machine code 2 Translator programs are of three kinds Compilers Interpreters and Assemblers Page 3 of 115 Www revision notes co cc What is compiler Compiler translates source code written in a high level programming language to object code which can be saved as an object code file and later run to execute the program Compiler does this b
113. work is not tied up for long periods of time gt Message is difficult to be hacked Disadvantages of packet switching gt Transmits at the speed of the slowest packet gt Packets must be reordered and reassembled at the destination Protocol A protocol is a set of rules which control the data transmission in a network Protocols specify the following requirements Type of data transmission i e whether the data transmission is serial or parallel For example errors would occur if one device has a serial connection and the other device expects a parallel connection Mode of data transmission i e whether the data transmission is full duplex half duplex or simplex Bit rate since both sending and receiving devices must send and receive data at the same number of bits per second Otherwise bits may be missed or counted twice Error checking i e whether the parity is odd or even whether echoing back is used or whether check sums are used Network protocols are divided into layers Protocols belonging to one layer carry out a specific function relating to data transmission International Organization for Standardization ISO Page 78 of 115 Www revision notes co cc RN released the OSI reference model in 1984 This standard divides the protocols into seven layers The model containing the protocol layers is known as the OSI reference model The protocols are implemented in the computer through software TCP IP is the mos
114. y scanning through the source code in one run What is interpreter Interpreter converts source code written in a high level programming language to machine language line by line and executes each line What is an assembler Assembler converts assembly language code into machine language What is object code Object code is the product obtained when source code is translated by a compiler Object code may almost be machine code or close to machine code Translated by Compiler Object Code Translated by Interpreter Machine Code Assembly Code Translated by Assembler What is an executable This is a compiled program which has a user interface and can run independently Three different times associated with an application program Design time compile time and runtime Page 4 of 115 Www revision notes co cc What is design time This is the time spent on developing a software application What is compile time This is the time spent on compiling source code What is runtime This is the time during which a software application executes This occurs after the compilation What is a routine A routine is a block of code which carries out a particular task Routines are either procedures or functions In the example given below Procedure and Function are routines Main Line 1 Procedurel x y Line 2 Answer Function x y Line 3 EndMain Line 4 Procedure a b Line 5 a b L

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