Home

A Sequence Diagram Editor for BlueJ

1. message of messages connected to them Figure 6 3 How the XML file is arranged All parts of a saved sequence diagram are arranged in a tree structure with the sequenceDiagram node as the root The XML file is arranged with a tree structure see figure 6 3 The node se quenceDiagram acts like the root All actors and objects in a sequence diagram are saved as child nodes to the root Each actor object has child nodes containing information about the lifeline destroy symbol and all messages belonging to the actor or object Each message also has a child node containing the information about its return message The sequence diagram contains a text representing the notes about this sequence diagram This note is saved as a child node to the root The number of actors and objects in a sequence diagram are arbitrary and also the number of messages belonging to an actor or an object 6 2 Design 33 Sequence Diagram Editor exempel sd E gt Figure 6 4 An example of a simple sequence diagram In figure 6 4 a simple sequence diagram is displayed The XML textual syntax for this sequence diagram will be lt xml version 1 0 encoding UTF 8 gt lt sequenceDiagram bluej shapes gt lt notes gt Notes about this Sequence Diagram This diagram is only an example lt notes gt lt actor startPoint 85 20 endPoint 95 60 name Actor BClass null hasDestroySymbol
2. A 2 Installation of the Plugin To install the editor as a plugin for BlueJ copy the Jar file Meditor jar into the lib extension directory of your BlueJ installation Next time BlueJ is started the plugin will appear in the menu of the BlueJ application A 3 Starting the Plugin If the editor is started as a plugin to BlueJ it is started from the menu in Blue Choose tools Sequence Diagram Editor to start the editor If the editor is started without BlueJ the jar file is executed to start the editor A 4 A Tutorial Creation of a Sequence Diagram 51 A 4 A Tutorial Creation of a Sequence Diagram When the editor has been installed and started a sequence diagram can be created This tutorial will illustrate when the editor is in BlueJ mode using a project called people2 which comes as an example with the BlueJ program The scenario de scribed in the sequence diagram will display a secretary registrating a new student adding him or her to the database First an actor is added to the sequence diagram This is done by clicking on the icon for an actor see figure A 1 The name of the actor is then changed to Secretary by double clicking on the actor or by choosing from the menu The menu of the actor is shown by clicking on the actor with the right mouse button Next step in the sequence diagram is the creation of a new student The Secre tary will create a new student to add to the database This is done by first cho
3. Today many courses in programming for beginners use problem solving based teaching also called prob lem based learning Though there are many people positive to this approach there are also people meaning that the biggest difficulty for anovice programmer is to ex press solved problems using a programming language Robins et al 2003 These people mean that problem solving is of course important but the student also has to learn the programming language how to use it and how to write programs for the solved problems 3 2 Coding and Design Analysis 17 3 2 Coding and Design Analysis When the problem has been analysed and solved the design phase of the pro gram system can start Before starting with the implementation the system has to be designed When students new to programming learn and hear about design they often find it unnecessary and do not realize the importance of design Because the programs they write in the beginning are so small it can be hard for them to see how significant the design is But it is really important that it is pointed out for them why design is so crucial Trying to explain how difficult impossible it would be to create a bigger system without any design is very important and also to show them examples of bigger systems Since most programming courses for beginners today use an object oriented language the significance of design grows since design is quite fundamental in object orientation To express the
4. addPerson and click OK The diagram will now look as in figure A 5 Sequence Diagram Editor tutorial sd feeScert Student tite AGS Figure A 5 The finished sequence diagram Now the sequence diagram is complete and all objects and messages have been added If the diagram has not been saved yet this is done by either press ing Ctrl S or choosing save save as from the file menu The name of the sequence diagram is typed and then click OK see figure A 9 The file of the diagram will be saved in the same directory as the project it belongs to that is the currently open project in BlueJ A 5 Adding Components to a Sequence Diagram 55 A 5 Adding Components to a Sequence Diagram If the editor is started the user can choose to create a new sequence diagram or open a saved one To create a new sequence diagram the diagram is drawn in the drawing area and later saved under the menu file save as Otherwise a saved sequence diagram is opened using the menu file open A 5 1 Adding an Actor To add an actor to the sequence diagram just click on the icon for an actor see figure A 1 and an actor will be added to the drawing area A 5 2 Adding an Object class chooser Figure A 6 If the editor is in BlueJ mode the user first has to choose the class of the new object the window to the left and then the name of the object the window to the right To add an object to the sequence diagram
5. of interaction diagrams sequence diagrams and collaboration diagrams 6 Chapter 2 UML A sequence diagram explains how operations are performed describing differ ent scenarios They show how different objects work together and what messages method calls are sent between them A sequence diagram shows time ordering between messages and the messages are organized chronological A sequence dia gram is shown in figure 2 3 redObject ClassRed blueObject ClassBlue MessageA MessageB MessageC Figure 2 3 An example of a sequence diagram Collaboration diagrams contain the same information as sequence diagrams but they concentrate on the role of the objects the relationship between the ob jects and the communication between them Instead of having an axis showing the ordering in time between the messages each message has a sequence number A collaboration diagram is shown in figure 2 4 1 1 MessageA 1 3 MessageC redObject ClassRed blueObject ClassBlue 1 2 MessageB Figure 2 4 Example of a collaboration diagram Both collaboration and sequence diagrams are best to use when different sce narios are being described The collaboration diagram emphasizes who is talking to whom and the time ordering of the messages gets a little clouded The se quence diagram on the contrary accentuates the time ordering of the messages though here the who is talking to whom situation gets obscured S
6. 2 1 Diagrams in UML 5 2 1 2 Class Diagrams To get an overview of a system its classes and the relationships between them a class diagram is used The relationship among the classes can be several differ ent kinds The three most used relationships are association generalization and aggregation An association between two classes is a labelled relationship A gen eralization is a hierarchical relationship between two classes meaning that one class is the parent of the other class as in an inheritance hierarchy An aggrega tion between two classes also called a dependency is a relationship meaning that one class depends on another in some way that if changing one class may lead to have to change the other class too Class diagrams are static in the way that they describe what parts interact and not what happens when they interact with each other Booch et al 1999 LeBlanc and Stiller 2000 Figure 2 2 An example of a class diagram 2 1 3 Object Diagrams The object diagram is very similar to the class diagram except that they show in stances objects instead of classes The object diagram models a set of objects and their relationship during a system snapshot An object diagram is very useful when for example explaining complicated relationships within a smaller part of a system LeBlanc and Stiller 2000 2 1 4 Interaction Diagrams Interaction diagrams describe dynamic aspects of a system and there are two kind
7. BlueJ calls this method sending an object of itself as an parameter This class later starts the editor by creating an object of the class SeqDiagramEditor SeqDiagramEditor This class starts the editor and creates menus icons the draw ing area etc It also handles all events that comes from the menus or if the user clicks on one of the icons DrawingArea This class contains most of the code and could be said to be the brain of the editor DrawingArea java implements the interfaces Action Listener EventListener MouseListener and MouseMotionListener DrawingArea 36 Chapter 6 A Sequence Diagram Editor for BlueJ keeps track of a lot of information e g what file is currently open what parts to draw in a sequence diagram and it also saves and opens a sequence dia gram to and from a file CurrentState This class is used by the Drawingarea to keep track of what to do next If a user selects e g a lifeline the current state is updated for the Drawingarea so it knows how to handle next event created by the user For example if a new message is to be created and the start point of the new message has been selected the class Message sets the CurrentState for DrawingArea to RUBBERBAND Then the DrawingArea knows how to be have and what action to take when the user makes his or her next choice Every class has a kind of state machine that tells the DrawingArea what the next step will be see figure 6 6 The class CurrentState defines
8. Class Diagrams coo yarn Sa a a a a o ara 2 1 3 Object Diagrams o o e 2 1 4 Interaction Diagrams 2 1 5 Behaviour Diagrams 2 1 6 Implementation Diagrams UML Diagrams in Education o 2 2 1 Educational Benefits for Using a Subset of UML Use Cases and their Scenarios o o Sequence Diagrams e e 3 Teaching and Learning Software Development 3 1 3 2 3 3 Programming and Problem Solving Coding and Design Analysis 2 2 2 22 nennen Syntax and Semantics o e e e 4 Teaching and Learning Object Oriented Programming 4 1 4 2 4 3 Object Oriented Programming vs Procedural Programming Different Teaching Approaches Using Java 2 2 2 Active Learning ara mn a ar ned 5 Sequence Diagrams in Education 6 A Sequence Diagram Editor for BlueJ 6 1 6 2 Requirements ee sn ee de ee ek Designs 4 2 0 6 4002 Gee wae Sa wl dhe eke NN O 0 JJ JU Nn HS rw 15 16 17 17 19 20 21 vi CONTENTS 6 2 1 The Graphical User Interface 28 6 2 2 Return Messages e 30 6 2 3 Sequences au un u e ee 31 6 2 4 Different Modes of the Editor 31 6 2 5 Creating a Plugin for BlueJ 31 6 2 6 File Management e 32 6 2 7 Automatic Consistenc
9. a number of different states e g NORMAL INSERT FIND_END_POINT and CHANGE These states are used by the different classes to set the state correct for the DrawingArea Entity This class is an abstract class that all parts belonging to a sequence diagram inherit from Message This class inherits from Entity and represents a message in a sequence diagram A message can go between two objects or actors but can also have the same object or actor as start and end point This class has an attribute saying whether it is a regular message or a return message Depending on the value of this attribute the message is drawn in different styles on the drawing area LifeLine This class inherits from the class Entity and represents a lifeline in a sequence diagram A lifeline is always associated with either an actor or an object DestroySymbol This class represents a destroy symbol for an object and it also inherits from the class Entity A destroy symbol is always connected to an actor or an object ClassEntity This is an abstract class that represents either an object or an actor in a sequence diagram It inherits from Entity and implements a few methods common for an actor and an object Actor This class inherits from ClassEntity and represents an actor in a sequence diagram SequenceObject As the class Actor this class also inherits from ClassEntity and an object in a sequence diagram is represented by this class 6 3 System Descriptio
10. and the return message belonging to it Then create a new object from the class Address as described before The look of the diagram will now be as in figure A 4 If a message an actor or an object has been added to the diagram but should be deleted this is done by clicking on the component with the right mouse button and a menu will appear Just choose delete from the menu and the component will be deleted from the sequence diagram Sequence Diagram Editor tutorial sd A Secralary new Student p newstudert l setAddrass p new Atdressi l L L I l l l l l I l l l Figure A 4 The student creates a new object of the class Address to be able to set its own address 54 Chapter A User Manual Next and last step in the sequence diagram will be the Secretary adding the new student to the database First we have to add an object of the class Database to the sequence diagram This is done by choosing to add a new object to the diagram by clicking on the icon for an object see figure A 1 Then choose which class to create the object from and write the name of the new object see figure A 6 Now the Secretary adds the new student to the Database by calling the method addPerson in the database To add this method call into the diagram first choose to add a new message click on the lifeline of the actor and then click on the lifeline of the database Then choose which method in the list
11. can be very helpful for the students trying to understand and learn about object orientation objects and the communication between objects in the system The three different teaching approaches described in section 4 3 all include the use of sequence diagrams in some way Since the major part of sequence diagrams describes the communication be tween objects and the time ordering among messages they can help a student both to understand an already designed system or help the student to design and anal yse his or her own new system If the students are to design a new system and for example use the model with role plays sequence diagrams will play a meaning ful part Since the role play produces different scenarios when the students play different classes cooperating to achieve certain goals the scenarios have to be doc umented in some way Since the purpose of sequence diagrams are to describe different scenarios the natural thing would be for the students in the role play to use a sequence diagram to document the scenario the role play resulted in If a se quence diagram is used for the documentation this diagram will help the students later in the design and the implementation of their system One other guideline when teaching object orientation is that students get a bigger system and try to un 25 26 Chapter 5 Sequence Diagrams in Education derstand it and later make changes to the system When the student gets a system and
12. click on the icon for an object see figure A 1 If the editor is in BlueJ mode the class of the object first has to be chosen see figure A 6 This is done by selecting one of the classes in the list and then click on the OK button After this the user has to fill in the name of the new object If a new name is not given the object will be given a default name like object A 5 3 Adding a Message To add a message to the sequence diagram click on the icon for a message see figure A 1 To select the start object of the message meaning the object making the method call to the end object click on the lifeline on this object or actor To select the end object of the message click on the lifeline of this object If the editor is in BlueJ mode the user has to choose a method This is done by selecting one method in the list and click on the OK button see figure A 7 If the option Show return messages is selected in the menu under option each added message 56 Chapter A User Manual public int sampleMethod int k Figure A 7 If the editor is in BlueJ mode and a message is added the user has to choose which method to add by selecting one from the list will get a return message belonging to it If the return message has a type this will be added as a label to the return message A 5 4 Adding a Destroy Symbol A destroy symbol can be added to an object or to an actor This is done by clicking on the obje
13. correcting many of the grammar mistakes 43 References Beck 1989 Beck K 1989 A laboratory for teaching object oriented think ing In Object Oriented Programming Systems Languages and Applications http c2 com doc oopsla89 paper html Bj rkander 2003 Bj rkander M 2003 Det v ras f r uml 2 0 Elektronik i Norden 10 Booch et al 1999 Booch G Rumbaugh J and Jacobsson I 1999 The Uni fied Modeling Language User Guide Addison Wesley Longman Inc du Boulay 1989 du Boulay B 1989 Some difficulties of learning to program In E Soloway amp J C Spohrer Eds pages 283 299 Fowler and Scott 1997 Fowler M and Scott K 1997 UML Distilled Apply ing the Standard Object Modeling Language Addison Wesley Group 2004 Group O M 2004 Interim ftf report of the uml 2 0 super structure finalization task force Technical report Object Management Group http www omg org Harley et al 1998 Harley H D Seals C D and Rosson M B 1998 A formative evaluation of scenariobased tools for learning object oriented design Webpage www acm org crossroads xrds5 1 eval html last checked 040302 Hussman 2002 Hussman D 2002 Test first design with uml a picture is worth a thousand programmers In Workshop on Teaching in XP WTiXP2002 http www cwi nl wtixp2002 cfp Jensen 2003 Jensen R W 2003 A pair programming experi ence Crosstalk Th
14. design UML diagrams are often used Since the UML is composed of nine different diagrams it is rec ommended that only a subset of the diagrams is used so the student does not find it too overwhelming Design is just as problem solving something that must be practiced and exercised There are many different methods to teach design and many are connected to object oriented design This will be further discussed later in section 4 3 3 3 Syntax and Semantics When learning a new programming language the student first has to learn what everything means and how it is written This is when syntax and semantics are the crucial concepts Shortly the syntax of a language can be described as how the dif ferent expressions statements and program units are written The semantics of the language can be described as the meaning of those expressions statements and pro gram units Syntax and semantics are closely related and it is often found easier to understand explain syntax then semantics As Robert W Sebesta Sebesta 1999 says this is partly because a concise and universally accepted notation is available for syntax description but yet there is none developed for semantics To clarify the difference between semantics and syntax lets take an if statement written in the syntax of the programming language C if lt expr gt lt statement gt How we write this statement form is controlled by the syntax and this is the correct syntax for an if st
15. diagram Of course it could be implemented in later versions of the editor 41 42 Chapter 8 Summary and Conclusions Since the purpose of the editor is to be used as a plugin to BlueJ it is designed to be run in two different modes BlueJ mode on or off When it is run in BlueJ mode the editor is connected to a project in BlueJ Then the user can only draw sequence diagrams describing a given project including its classes and methods When drawing the sequence diagram the user gets to choose from existing classes and their methods This will hopefully help the student draw correct sequence diagrams describing their systems If the editor is run with BlueJ mode off the user can draw sequence diagrams containing any classes and methods One thing missing in the editor is the possibility of code generation If the user draws a diagram and suddenly realizes that he or she is missing a class or a method he or she has to go back to BlueJ and implement the class or method It would be very convenient for the user if he or she just could add the class or method in the editor and then the code would automatically be generated Code generation could also be helpful if the user draws a sequence diagram and code was generated based from the diagram All classes used in the diagram were au tomatically created and code stubs for the methods where generated This would save lots of time for the user letting him or her focus on more important parts of the i
16. false hasCreationMessage false gt lt message mess setVisible startPoint 90 105 endPoint 290 115 isCreateMessage false isReturnMessage false startEntity Actor endEntity null sequenceIndex null returnMessage notNull gt lt message mess startPoint 290 135 endPoint 90 145 isCreateMessage false isReturnMessage true startEntity null endEntity Actor gt lt message gt lt lifeline startPoint 86 65 endPoint 94 420 gt lt actor gt lt object startPoint 240 20 endPoint 340 60 name canvas length 101 BClass BClass Canvas hasDestroySymbol true hasCreationMessage false gt lt destroysymbol startPoint 281 341 endPoint 301 361 gt lt message mess setVisible startPoint 90 105 endPoint 290 115 isCreateMessage false isReturnMessage false startEntity null endEntity canvas sequenceIndex null returnMessage notNull gt lt message mess startPoint 290 135 endPoint 90 145 isCreateMessage false isReturnMessage true startEntity canvas endEntity null gt lt message gt lt lifeline startPoint 286 65 endPoint 294 351 gt lt object gt lt sequenceDiagram gt 34 Chapter 6 A Sequence Diagram Editor for BlueJ Since the program can be in two different modes see section 6 2 4 BlueJ mode on or off the saving procedure also differs a little When the program is in BlueJ mode the sequence diagram is always saved in the
17. object and then an activation for it Last is the notation for a message sent between the objects A sequence diagram has two dimensions time which is represented by the vertical dimension and different objects and actors that are represented by the hor izontal dimension In most cases time proceeds down the page though if desired the dimension may be reversed The ordering among objects in the horizontal di mension is of no significance and arbitrary But often the objects are ordered in such a way that the call arrows messages are arranged to point in the same direc tion to the right but in some cases this is not possible Each object has a vertical dashed line which is called the lifeline of the object The existence of the object is represented by the lifeline at a particular time Rumbaugh et al 1997a The life line can show whether the object is being created or destroyed during the shown scenario and when and for how long the object is active The activity of the object is shown as a tall thin rectangle which starts at the initiation of the activation and ends when the object is not active anymore If the object is being destroyed this is marked with a big X and the message destroying the object points at the X and the lifeline is ended at this point If the object is created this is shown by letting the message creating the object point to the object symbol This is shown in figure 2 6 An object that exists throughout the
18. sequence di agrams Sequence diagrams based on scenarios are powerful in many aspects but are maybe most associated with the specification and analysis phase Sequence diagrams are also very powerful and useful when describing different test cases during the testing phase One of the simplest but also the most powerful change is the introduction of references to other sequences This gives the opportunity to break down a sequence into smaller sequences and then have references to it from other connections All this leads to increased usability of sequence diagrams within UML Bj rkander 2003 The increased interest for sequence diagrams in the context of UML is also reflected in education when UML is adopted Teaching and Learning Software Development When teaching software development there are some concepts that are essential and it is important for the teacher to explain and clarify these concepts for the student Most people think that software development is just about sitting in front of the computer and writing code They do not understand the concepts design analysis problem solving etc It is very important that a student new to programming learns and understands these concepts and realizes the meaning of them Many students find it less interesting with design and does not fully understand the importance of design They just want to take the problem and write the code for it without making any design or thinking about the best
19. the documentation belonging to the system it will surely make it easier for the student to understand the overall program flow if a sequence diagram is used Then the student can see how the different objects cooperate and how messages are sent between them This will certainly facilitate the understanding of the system for the student and help him or her see the overall program flow If there were no sequence diagram to help explain and show the program flow of the system the student had to read and try to understand the code to get the whole picture If the student were a beginner in programming and maybe also in object orientation this would for certain not be an easy task When students in a group together are supposed to design a system with its classes and methods the process is simplified if sequence diagrams are used When several people students sit together discussing for example the design of a system it is very easy to misunderstand or misinterpret each other if only words are used If the group wants to be sure that no misinterpretations are made and that everybody is talking the same language it is very good to draw a picture Hussman 2002 When designing an object oriented system this picture very natural becomes a sequence diagram since the discussions in the design phase certainly are concen trated around classes and the communication between them If it is the students first programming course it is even more ex
20. understanding Taking away the old picture of teaching and learning when the teacher talked and the students listened and hopefully learned what they where supposed to learn Both techniques described above often use sequence diagrams or a simplified version of them for the documentation In chapter 5 the use of sequence diagrams in education will be further discussed and described Sequence Diagrams in Education Since object oriented languages have become the leading programming languages in the beginner s programming courses instead of procedural programming lan guages UML has begun to play a bigger part in the education Relating to previous sections about teaching object orientation and the guide lines mentioned together with the new approach with active learning sequence diagrams become very important and useful Since object orientation is much about design and the understanding about objects and classes and the connection between them UML is widely used When beginners start with object orientation one complicated thing is how to understand and see the communication between different objects to understand how objects cooperate to accomplish a given task and how messages are sent between the objects As Fowler and Scott point out Fowler and Scott 1997 it can be very difficult to understand the program flow in an object oriented system especially for beginners new to object orientation Here sequence diagrams
21. way to solve the problem In the beginning this can work but when the problems get more complicated and the systems to implement get more complex this method will fail So it is very important that the teacher lets the students realize the importance of design and have them see the positive side of it Many authors have agreed that the most important thing when teaching learning programming are the issues of problem solving design and expressing a solution or design as a program Robins et al 2003 Learning to program is not easy and it involves getting complex new knowl edge and practical skills Du Boulay du Boulay 1989 describes five sources of difficulty that must be overcome These five domains are overlapping and some times all these new things can come as a shock for the student These domains are General orientation What programs are for and what can be done with them Understanding that programs are usually written for a purpose with respect to some task problem or specification The notional machine A model of the computer as it relates to executing pro grams Getting an overview of the computer how it works and how the programs implemented are executed 15 16 Chapter 3 Teaching and Learning Software Development Notation The syntax and semantics of a particular programming language Learn ing to understand and use the new programming language Learn how to write different statements and how to c
22. Master thesis in Computing science 20 credits A Sequence Diagram Editor for BlueJ Matilda stling lt c99mog cs umu se gt Department of Computing Science Ume University 10th May 2004 Abstract Today most programming courses for beginners use an object oriented language This has led to many new learning tools theories and methods for teaching object orientation One such new tool is BlueJ which is developed to teach Java and object orientation for beginners BlueJ does not have any support for drawing se quence diagrams and this thesis describes the development of an editor for se quence diagrams The editor is developed as a plugin for BlueJ and designed to be used by beginners This paper describes the design and implementation of the editor and it contains a user manual for the editor In this thesis it is also talked about UML diagrams in general and more specific about sequence diagrams The use of sequence diagrams in education of object oriented thinking is described and advantages are pointed out Object oriented education is discussed and different teaching methods are addressed Contents 1 Introduction 1 1 1 2 1 3 Background os 2 u 20 2m as ee sn Rn e The Purpose of this Master s Thesis Thesis Outline s tio gy ata Kara Pa eae De bars 2 UML 2 1 2 2 2 3 2 4 DiagramsinUML o oo e e 2 1 1 Use Case Diagrams o nennen 2 1 2
23. The editor only provides notations for the most basic parts of a sequence dia gram What the basic parts of a sequence diagram are is only based on my own opinion and can of course be discussed The editor has support for drawing ac tors and objects with lifelines It provides two different types of messages regular synchronous messages and return messages The reason for only supporting syn chronous messages is because the editor is designed for beginners and they often only use this kind of messages If the editor would support all possible messages of the UML the user would probably find it complicated to know what message to use if there were too many possibilities Since beginners new to object oriented programming often write sequential programs the editor also provides the possibil ity to have the messages creating a sequence Through this sequence of messages the program flow is easy to follow and understand Return messages are also sup ported and the user can choose whether he or she would like to show or hide the return messages Other notations that the editor has support for is destroy symbols and create messages The possibilities of having activation boxes are missing in the editor and this could be seen as a drawback The explanation for this is that it showed to be quite difficult to get them right and it did not seem too important to offer this functionality for beginners since they do not bring anything very impor tant to a sequence
24. agrams have shown to be appreciated both by experienced programmers and by novices Though collaboration and sequence diagrams almost contain the same information sequence diagrams more clearly show the program flow and helps the student understand the system A sequence diagram is also often quite structured and it is easy to read and follow the program flow A collaboration dia gram can easily become a little indistinct if 1t gets too big and complex including many objects and messages This makes the messages cross each other and makes 1t hard to arrange the objects in a structured way leading to a diagram being diffi cult to interpret Sequence diagrams and their use in education together with active learning will be further described in chapter 5 2 3 Use Cases and their Scenarios Use cases are used to describe sequence of events and to show how the system is supposed to interact with an actor a user of the system A use case is often just a plain text documentation that can be obtained from for example the requirements document A use case is created for every major functionality of the system Use cases are very useful in the design phase since they describe what a system does without having to say how the system should achieve a certain task and how to 10 Chapter 2 UML implement it LeBlanc and Stiller 2000 Scenarios can be used in many situations for example in the analysis of the requirements in the software design or i
25. also connected to the keyboard if the user for example wants to use Ctrl S instead of choosing save from the menu The same functionality is also included in Blue The icons At the left side in the window four icons are placed These icons repre sents from top down an actor an object amessage and notes for the sequence diagram The three first mentioned icons are the most common parts of a se quence diagram and because of this it seemed natural to give them each an icon In this way the user easily can create for example an object without having to use the menu The icon for notes is placed in the left bottom a little bit away from the other icons because it has a different functionality In BlueJ each project has a note belonging to it where the user can write information about the project To be consistent to BlueJ the editor also has a note where the user can save information belonging to a certain sequence diagram The drawing area The drawing area where the sequence diagram is drawn is placed to the right in the window The background is white and the dif 30 Chapter 6 A Sequence Diagram Editor for BlueJ ferent parts of the sequence diagram are drawn in black Simple and easy to read The drawing area has a default size from the start but if the user draws a sequence diagram that is bigger than the drawing area scrollbars are added automatically Then the user can scroll the drawing area if the diagram is too big When an actor o
26. at io nal com Together see www borland com together etc The big draw back with these editors is that they are too complicated for beginners to use since they are designed to be used by experienced programmers If a beginner new to programming and UML should use any of these programs he or she would only get confused and intimidated probably leading to less interest in the area Today there are less complicated editors for UML too for example MS Vi sio developed by Microsoft and Violet see www horstmann com violet MS Visio has a library for drawing UML diagrams but the program does not un derstand the diagrams This leads to that the components can be arranged in any way and there is no check for correctness of the diagrams Violet is an editor de signed to be used by students and it is quite easy to learn and understand Violet has the same drawback as MS Visio it does not interpret the diagrams and the components can be combined in any way If a student draws a sequence diagram it would be helpful if the editor could make a consistency check against a class diagram of the system Another drawback with the editors mentioned is that they are not platform independent MS Visio for example does only work together with Windows Today many courses in programming for beginners use Java as the object oriented programming language and BlueJ as an editor for writing programs in Currently BlueJ does not have any support for drawing sequence d
27. atement written in C The semantics of this statement form is that if the expression the current value of it is true then the statement will be executed Many different studies have shown that novice programmers who know the 18 Chapter 3 Teaching and Learning Software Development syntax and semantics of individual statements in a programming language often find it very hard to combine these statements into a program They have solved the problem by hand but they can not write an equivalent computer program for the solution Robins et al 2003 So learning the syntax and sematics of a pro gramming language does not mean that the student will be able to write programs using the given language First he or she has to learn how to translate the solved problem into code by combining different statements Teaching and Learning Object Oriented Programming 4 1 Object Oriented Programming vs Procedural Programming Today most programming courses for beginners use an object oriented language instead of a procedural language One of the main reason for the change in pro gramming language is that the proponents of object orientation are claiming that object oriented thinking is more natural than procedural thinking Neubauer and Strong Neubauer and Strong 2002 write about the theory that object orientation is more natural and base this theory on the idea that the world we live in and experience is filled with things or object
28. ced between message B and message B s return message Then message A will be added to the sequence after message B and all positions for messages and return messages belonging to the sequence will be automatically arranged 6 2 4 Different Modes of the Editor Since one requirement was that the editor should be a plugin for BlueJ and that a sequence diagram should be connected to a certain project the editor is developed so it can be run in two different modes BlueJ mode on or BlueJ mode off If the editor is in BlueJ mode the sequence diagram that is being drawn will be connected to the current open project in BlueJ Then the user must choose classes and methods belonging to the project If the editor is not in BlueJ mode the user can draw a sequence diagram that contains objects messages etc that are not yet implemented If the program is started from BlueJ as a plugin the default is that the editor is in BlueJ mode The user can change the mode under option in the menu The editor can also be started as an independent program and then it is used to draw arbitrary sequence diagrams 6 2 5 Creating a Plugin for BlueJ When creating a plugin for BlueJ I got a lot of help from the webpage for BlueJ see www bluej org They had a number of tutorials and examples When the editor is in BlueJ mode it has to get information of the current open project For example what classes exist and what methods each class contains so the user can choose what c
29. classes or objects and it does not im plement an operation on an object K lling and Rosenberg 2001 Another thing with Java is its support to deal with input and output which is huge and complex and can lead to difficulties for beginners A proposal to solve this is that the teach ers provide students with classes for I O that encapsulate the complexities in Java Another approach is that the standard I O is just avoided until the students are able to understand and use it Lewis 2000 There are more guidelines for teaching object orientation that often come up One is that the students in the first stage do not start with a blank screen but instead make changes to already existing code and see what the result of the changes are It is also recommended that students read code to get a sense of well written programs and learn about good style and idioms K lling and Rosenberg 2001 It is really not easy for a student to write good code if he or she never got the opportunity to read well written and structured code 4 3 Active Learning To fulfil all or at least some of the guidelines mentioned in section 4 2 when teaching object oriented thinking some newer approaches have been adopted One widely used approach is active learning Active learning means that the student instead of just receiving new knowledge from the teacher instead gets a problem and solve it often with some guidance from the teacher This type of education forces the lear
30. ct or actor with the right mouse button and a popup menu will appear The destroy symbol is added by selecting create destroysymbol in the menu and then click on the lifeline of the object or actor where the destroy symbol should be placed A 5 5 Notes about the Sequence Diagram Figure A 8 The window where the user can write notes belonging to a sequence diagram Each sequence diagram has a note a text field belonging to it The note can contain information about the diagram for example if the user wants to point out something special about the diagram a general description of the scenario etc he or she can write it here To write notes for a sequence diagram just click on the A 6 Save and Open a Sequence Diagram 57 icon for notes see figure A 1 Then a window will appear see figure A 8 where the notes can be written Before closing the window click on the save button and the notes will be saved together with the sequence diagram A 5 6 Return Messages Every message that is added to a sequence diagram will automatically get a return message If the editor is in BlueJ mode the type of the return message will be added as the label of the return message The user can choose whether to display the return messages or not This is done under option Show return messages Return messages can be switched on and off during the development of a sequence diagram A message having the same object as its start and end object will not g
31. e same object in a row this will cause problems New messages can only be added at the end of the sequence and not in the middle of an already existing sequence Consistency check When a sequence diagram is opened it is checked against a BlueJ project But only classes are checked and not methods Moving components Sometimes when different objects or actors are rearranged in the drawing area all attributes belonging to them do not get the correct new position Creation messages A creation message can not be in a sequence of messages Return messages When a regular message is added to the sequence diagram it gets a return message placed in the right positon But later on the user can move this return message to any position without any controll from the edi tor Inheritance If a classA inherits from classB all classB s public methods are also shown for classA But if classB inherits from classC classC s public meth ods should be shown for classA which is not the case The inheritance is just shown in one step in the editor
32. e Journal of Defense Software Engineering http www stsc hill af mil crosstalk 2003 03 jensen html K lling and Rosenberg 2001 K lling M and Rosenberg J 2001 Guidelines for teaching object orientation with java In Innovation and Technology in Com puter Science Education 45 46 REFERENCES Kutar et al 2002 Kutar M Britton C and Barker T 2002 A comparison of empirical study and cognitive dimensions analysis in the evaluation of uml diagrams In PPIG Psychology of Programming Interest Group LeBlanc and Stiller 2000 LeBlanc C and Stiller E 2000 Uml for undergrad uate software engineering In Consortium for Computing Sciences in Colleges Lewis 2000 Lewis J 2000 Myths about object orientation and its pedagogy In SIGCSE 2000 http duke csc villanova edu lewis presentations mythsPaper html Miller 2001a Miller G 2001a Conditional logic in sequence diagrams http www 106 ibm com developerworks library j jmod0605 index html last checked 040302 Miller 2001b Miller G 2001b Introduction to sequence diagram http www 106 ibm com developerworks library j jmod0508 index html last checked 040302 Mrozek et al 2002 Mrozek Z Mrozek B and Adjei O 2002 Teaching object oriented software engineering with uml In 3th EAEEIE Annual Con ference on Innovation in Education for Electrical and Information Engineer ing EIE Neubauer and Strong 2002 Neubaue
33. e To delete a destroy symbol click on it with the right mouse button and choose delete from the popup menu Move To move a destroy symbol select it by clicking on it The destroy symbol will then be drawn in red and a handle will appear in the middle To move the destroy symbol click on the handle and drag the destroy symbol with the left mouse button down to the new position The destroy symbol can only be moved up or down along the lifeline it belongs to A 7 5 Lifeline The length of a lifeline can be changed To change the lifeline first mark it by clicking on it The lifeline will then be drawn in red and a handle will appear at the end of the lifeline To change the length of the lifeline click on the handle and drag the handle to the new position for the end of the lifeline The handle can only be moved vertical along the lifeline 60 Chapter A User Manual A 8 Known Bugs There are a number of known bugs in the editor and surely a number of unknown too Since the program still needs some adjustments and more functionality there are some features left to implement One of the biggest bug is that the program is not all waterproofed it is not that hard to have it crash If the editor is correctly used it works OK but if the user starts to test the program there will probably happen strange things The known bugs in the editor are Sequences If a sequence contains two messages which are messages back to th
34. e diagram does not exist in the project anymore this object of the missing class is drawn in red in the diagram and the user gets a warning message from the editor 6 2 8 Creation Messages Sometimes an object is created by another object during a displayed scenario in a sequence diagram and this functionality is provided by the editor To create a new object or make a creation message the user first chooses to add a new message He or she selects the start object meaning the object going to create the new object But instead of selecting the end object for the message the user clicks with the right mouse button and then gets to choose which object to create The editor then creates the new object and places it at the end of the creation message 6 3 System Description 35 6 3 System Description If all classes and interfaces were to be described it would take up too much space so only the most important and interesting classes will be described All documen tation for the program can be found at http www cs umu se c99mog javadocs A class diagram including the most important classes can be seen in figure 6 5 CurrentState DestroySymbol SequenceObject Figure 6 5 A class diagram describing the most important parts of the system EditorExtension This is the main class If the program is started from BlueJ the editor is not started using main but another method called startup To start the extension
35. er of occasions when a collaboration diagram is better then a sequence diagram 2 2 1 Educational Benefits for Using a Subset of UML A class diagram is useful in the way that it models the composition of classes in a system Showing the different relationships between the classes and the elements being part of each class A class diagram gives a static view of the system though a system can have many class diagrams showing different structural aspects of the system For students having difficulties understanding inheritance which is a basic concept in object orientation between classes a class diagram can help It also shows how the classes depend upon each other and how the system is composed An object diagram reminds very much of a class diagram and has the same advantages The big difference is that instead of showing how different classes depend upon each other an object diagram shows instances of classes objects An object diagram contains values of different attributes making it possible for students to understand and see the relationships between objects at a given time Use case diagrams are used to show how the system interacts with a user and are commonly used in the design phase of a system A use case diagram is useful for students when designing the new system program and modeling the behaviour 2 3 Use Cases and their Scenarios 9 of the system towards a user This kind of diagram is good since it hides much of the functionalit
36. erline the structures of different objects in a system including their classes interfaces at tributes and relations between them The diagrams belonging to the static view are class diagrams object diagrams use case diagrams and implementation diagrams component and deployment diagrams The dynamic models also called the be havioural models emphasize the behaviour of different objects in a system includ ing their methods interactions collaborations and different states The diagrams included in this view are behaviour diagrams state chart and activity diagrams and interaction diagrams sequence and collaboration diagrams The following sections will briefly describe the different diagrams in UML and in what situations to use each diagram 2 1 1 Use Case Diagrams Use case diagrams describe what a system does and are closely connected to sce narios Scenarios will be described in section 2 3 They can be thought of as a summary of scenarios for a single task or goal Use case diagrams are best when developers are communicating with clients since they are relatively easy to under stand and relate to Use case diagrams are also useful when designing the system when the requirements are made and for generating different test cases for use in the testing phase Booch et al 1999 Cancel Appointment Make Appointment Schedula Request Medication j q Doctor Figure 2 1 An example of an use case diagram atient
37. et a return message A 5 7 Creation of a sequence Messages added to a sequence diagram can be arranged in a sequence All mes sages including return messages in a sequence will automatically be arranged with the same distance between them If a message in a sequence is removed the messages after the removed message will be removed from the sequence To add message M2 to a sequence after message M1 message M2 s start point has to be placed between message M1 s endpoint and its return message If this is done message M2 will be added to the sequence and all messages and return messages in the sequence will automatically be arranged A 6 Save and Open a Sequence Diagram gt Write the name for the file Figure A 9 If the editor is in BlueJ mode and the sequence diagram should be saved the user just has to fill in the name of the file To save a sequence diagram chose file save as save If the editor is in BlueJ mode only the filename has to be filled in see figure A 9 The file of the sequence diagram will be saved in the same directory as the project it belongs to 58 Chapter A User Manual If the editor is not in BlueJ mode the user chooses the name of the file and the directory where the file should be saved To save a sequence diagram the user can also press Ctr1 S To open a saved sequence diagram choose file open Then choose which file to open and click OK If the editor is in BlueJ mode only the
38. files belonging to the currently open project are shown To open a sequence diagram the keyboard can be used by pressing Ctr1 0 A 7 Moving Deleting and Editing A 7 1 Objects Delete To delete an object click on the object with the right mouse button and choose delete from the popup menu When deleting an object all attributes belonging to it will also be deleted such as messages destroy symbol life line etc Rename An object can be renamed in two different ways The name can be changed via the menu that appears when the object is clicked on with the right mouse button The name can also be changed by double clicking on the object Move To move an object first select the object by clicking on it The object will then be drawn in red and a handle a small square will appear To move the object click on the handle and drag the object with the left mouse button pressed down to the new position When the mouse is released all objects and actors in the sequence diagram will be rearranged automatically and the distance between them will be the same A 7 2 Actors Delete To delete an actor click on the actor with the right mouse button and choose delete from the popup menu If an actor is deleted all attributes belonging to 1t like messages destroy symbol lifeline etc will also be deleted Rename An actor can be renamed in two different ways The name can be changed via the menu that appears when the actor is clicked on with t
39. g and Rosenberg 2001 Lewis 2000 Con sidering the opinion that it is harder for students to think in an object oriented way rather than in a procedural way the strategies for teaching object orientation really has to help the students to think in an object oriented way The students have to learn to think and program with objects Neubauer and Strong 2002 Since all this is rather new there are several different theories and strategies about how to best teach object oriented thinking and it is hard to say which strategy is the best Today most programming courses for beginners use Java as the programming language Next section 4 2 describes different teaching approaches for object orientation with Java as the programming language 4 2 Different Teaching Approaches Using Java There are some guidelines that are often mentioned in many articles about teach ing object oriented programming and thinking to beginners with Java as the pro gramming language The most common approaches are Objects first and Ob Jects early which point out the importance of that students first of all get the un derstanding of objects when learning object oriented programming and thinking Though there is no scientific evidence or very little to support this theory most teachers and textbooks today are following this approach and start with objects early K lling and Rosenberg 2001 Ralph Westfall Westfall 2001 on the other hand says that this is n
40. generation meaning that if the user draws a sequence diagram the program should create code based on the drawn sequence diagram For example when the user is in BlueJ mode and suddenly realizes that he or she would need a new class or a new method in a class Instead of having to go back to BlueJ and create the class or method the user could just add the class or method to the sequence diagram and the editor would then generate the code for the method or class Since the editor is mainly supposed to be used by beginners there are a lot of notational possibilities of the UML that have not been implemented If the editor is to be used by more experienced programmers the editor has to offer more notational possibilities Activation boxes are not implemented in the editor since the conclusion was that this functionality was not very important for beginners If the editor is to be further developed activation boxes should be implemented and also the possibility for each actor or object to have a number of activation boxes If the drawn sequence diagram gets too big scrollbars are added to the drawing area A function that could be beneficial to have would be some kind of zoom so the user can zoom in and out Then the user can zoom out if he or she would like to look at the whole diagram at once or zoom in to look at a smaller part of the diagram in more detail Related Work There exist a number of editors for UML e g Rational Rose see www r
41. h et al 2001 OCL can be used for different intentions Rumbaugh et al 2001 e To specify invariants on classes and types in the class model e To specify type invariant for Stereotypes e To describe pre and post conditions on operations and methods e As a navigation language e To describe guards e To specify constraints on operations OCL is often used to show constraints for a message in a sequence diagram The given constraint says that it should only be executed if a special condition is fulfilled and OCL is used to express this condition OCL is a typed language so each expression must have a type A String can not be compared to an Integer in OCL and there is a set of predefined types in OCL that can be used when writing expressions using OCL There are also predefined operators keywords and the like in OCL Rumbaugh et al 2001 In later versions of UML sequence diagrams have come to have a more promi nent meaning In the specification for UML 2 0 that was recently released summer 2 4 Sequence Diagrams 13 ObjectA ObjectB ObjectC ObjectD I value gt 0 insertValue l l 4 increaseValue l Figure 2 7 Two different sequence diagrams The one to the left illustrates a message with a condition value gt 0 and the other one illustrates a loop The asterisk tells that there are a loop and the 4 tells that the number of iterations are four of 2003 Group 2004 one new thing was the increased potential for
42. he right mouse button The name can also be changed by double clicking on the actor Move To move an actor first mark it by clicking on the actor The actor will then be drawn in red and a handle a small square will appear To move the actor A 7 Moving Deleting and Editing 59 click on the handle and drag the actor with the left mouse button pressed down to the new position A 7 3 Messages Delete To delete a message click on the message with the right mouse button and choose delete from the popup menu The message will then be deleted If the message has a return message this return message will also be deleted Rename There are two ways to rename a message The message can be renamed by clicking on the message with the right mouse button and choose change message from the popup menu The message can also be changed by double clicking on it Return messages can also be renamed in the same way Move If a message is selected by clicking on it a handle appears By clicking on this handle and dragging it the message or return message can be moved vertically Creation message If a message is to create a new object this is done by first se lecting the start object for the message the object that is going to create the new object Then click with the right mouse button and the editor will let the user choose which new object to create The new object will then be added to the sequence diagram A 7 4 Destroy Symbol Delet
43. iagrams and there exists no editor that works integrated with BlueJ If the student using BlueJ would like to draw a sequence diagram he or she has to use some editor not con nected to BlueJ at all Doing so there will be no consistency check against the implemented classes and methods in BlueJ and the correctness of the diagram will not be controlled The editor developed in this thesis is hopefully easy to un derstand and use It is very uncomplicated to install and since it is implemented in Java it is just as BlueJ platform independent The editor is connected to BlueJ and the students using it can draw sequence diagrams describing their implemented classes and methods The editor always checks against existing classes and meth ods resulting in a correct and consistent sequence diagram 39 Summary and Conclusions In this paper the development of an editor for sequence diagrams has been de scribed The editor is designed to be used by beginners to programming and im plemented as a plugin for BlueJ Since the editor is mainly to be used by beginners the design has focused on making the editor easy to use and learn instead of having it contain a lot of functionality which would make it more complicated to use es pecially for beginners The plugin is easy to install into BlueJ just copy the jar file into the correct directory of BlueJ see section A 2 in the appendix Then the editor is started from the menu of the BlueJ program
44. ifications and for complex scenarios Sequence diagrams are used to model use case scenarios protocols in a framework subsystems classes and method logic Miller 2001b Or as Fowler Fowler and Scott 1997 explain the role of sequence diagrams One of the hardest things to understand in an object oriented pro gram is the overall flow of control A good design has lots of small methods in different classes and at times it can be tricky to figure out the overall sequence of behaviour You can end up looking at the code trying to find the program This is particular true for those new to objects Sequence diagrams help you to see that sequence The sequence diagram is very attractive since it permits a lot of useful infor mation to be shown at the same time One thing is that the objects interacting with each other in the described scenarios can be ordered in such a way that the interaction is easier to understand and follow Another good thing with se quence diagrams is that the lifeline of the object can point out the activity of the 2 4 Sequence Diagrams 11 object in isolation Last and maybe most important is the way that sequence dia grams show the sequence of execution and the distribution of execution between objects Fowler and Scott 1997 Object A Actor B Figure 2 5 The different notations in a sequence diagram First the notation for an object is shown then an actor In the middle is a lifeline for an
45. lass name Responsibilities and Collaborators and are widely used for teaching novice programmers the concept of object oriented thinking and design Beck 1989 Often the pro cess starts with identifying the classes in the future system and making a CRC card for each class Then the responsibilities and collaborators of the object are added on the cards Now the students can use the CRC cards to 4 3 Active Learning 23 illustrate different scenarios in the future system and document these scenar ios This is often done using some kind of role play where the students play different classes in the system The responsibilities and collaborators of the different objects are surely to change during the session and can easily be adjusted during the session CRC cards are suitable for groups of students and the groups must not be too big since it will then be hard to engage all students actively in the session Four to six students have shown to be a good size of the groups Nordstr m and B rstler 2002 Since the role play ses sions will create different scenarios describing the behaviour of the system it is a good idea to have one or more students documenting the role plays Sequence diagrams are often used when documenting the different scenarios resulting from the CRC sessions The main purpose with active learning is to include the student more in the learning process and making him or her more active in the seeking for new knowl edge and
46. lass or method to add to the sequence diagram For this BlueJ provide an interface that makes it quite easy to integrate the editor with the BlueJ program I started with adding the editor to the menu in BlueJ and when the editor starts it receives an object of the BlueJ program Through this object the editor gets access to the current open project and its classes methods etc 32 Chapter 6 A Sequence Diagram Editor for BlueJ 6 2 6 File Management There is a number of ways and methods to use when implementing the saving of a sequence diagram for example as a plain text file using XML etc It seemed very complicated to save them as plain text or some kind of combination of numbers since there is quite a lot of information that must be saved and it is easy that some thing goes wrong If you want to change something later on like remove or add an attribute that can be quite complicated Since I have never used XML it seemed like a good idea to use and learn about XML One positive thing about XML is that it is very easy to add or remove things during the development Changes are easy to make which would have been very hard if the diagrams for example had been saved as plain text can have any number of Each sequenceDiagram actor and objects sequenceDiagram object actor message message Each message Each object actor message message has a return can have any number
47. mplementation then writing new classes and methods On the other hand writing new classes and methods is not as intuitive and easy for beginners to programming as it seems to experienced programmers who often find this process quite boring and time consuming But if the editor later should be extended and include more functionality for more experienced programmers code generation would be a good functionality to add When implementing this kind of program it feels like it is never completed There is always some new functionality that could be added changed or removed The editor today hopefully provides enough functionality for a beginner in pro gramming to draw sequence diagrams in and is not too complicated or hard to un derstand and use Since the editor has not been tested with any appropriate users meaning beginners in programming this theory is only theoretical and should of course be further investigated Studies should be made with beginners to see how they find the editor and what improvements should be made to the editor Acknowledgements I would like to thank Jurgen B rstler at the Department of Computing Science at Ume University for all his help and ideas during the development of this thesis and for the help with the oral presentation I would also like to thank Claes Gahlin for his help and support during the development of this paper Finally I would like to thank my mother Monica stling for reading this thesis and
48. mponents and connections 2 2 UML Diagrams in Education The UML with its nine different diagrams is extremely large and offers many no tational possibilities When students new to object orientation and programming are trying to learn and use UML they can easily be confused and find it difficult to use UML It easily happens that they miss the big picture which is very important for understanding the goals and processes of software engineering Though UML is very complex with a lot of rules for syntax and semantics the most important core of the language is quite easy to learn and understand which is pointed out by LeBlanc and Stiller LeBlanc and Stiller 2000 When students start to use UML they only need to use a subset of the nine diagrams in UML or otherwise the students would be overwhelmed with all the possible notations The subset has to offer the student enough of notational possi bilities so he or she can model a software system without getting confused Which subset of UML to use in education is under discussion and there are many pro posals of suitable subsets of the UML The class diagram the sequence diagram and or the collaboration diagram appear to be the most used diagrams in education 8 Chapter 2 UML These diagrams would be enough for beginners in programming and make it possi ble for the students to document the software systems without finding it confusing and too hard Others wish to include more diagrams in the s
49. n 37 SDFilter This class is used when saving and opening files in the editor The filter only make files with the extension ds visible for the user sd 9 gt DRAGGING_START Figure 6 6 The state machine for an object of the class DestroySymbol When the object has been created and inserted to the sequence diagram it can toggle between the two states NORMAL and DRAGGING_START The state INSERT only appears when the destroy sym bol is added to a sequence diagram When the destroy symbol is added the state is updated to NORMAL If the user marks the destroy symbol by clicking on it the state is updated to DRAGGING_START and the destroy symbol can be moved by the user If the destroy symbol is unmarked by the user the state is updated back to NORMAL 38 Chapter 6 A Sequence Diagram Editor for BlueJ 6 4 Future Work There are a number of features that had not yet been implemented The main thing missing is an undo button The current solution for the user is to use the delete function if something goes wrong or gets into the wrong position Probably this can be quite frustrating for the user and an undo function must be seen to have high priority Another function that would be useful to have implemented is the possibility to print a sequence diagram Of course the user can take a screen shot and print that but it would be practical with a print functionality in the program There is also the possibility of code
50. n the implementation The first two men tioned are probably the most important and mostly used areas A scenario is used to describe a system s behaviour in a specific situation and can also be described as an instance of a use case It is created from a use case by looking at every pos sible outcome and creating a scenario for each possibility It is important to not only create scenarios for the normal system but also to show what will happen if an error occurs or if the system breaks down Scenarios can be documented just in plain text or sometimes using different states or logic From the different scenarios resulting from the use cases sequence diagrams can be drawn These sequence di agrams are often very useful in e g the design phase of the software development and the documentation of it 2 4 Sequence Diagrams A sequence diagram shows the interaction between objects in time The diagram displays the communication i e the objects participating in the interaction and the actual messages sent between them The sequence diagram focuses on the time ordering between the messages compared to the collaboration diagram that focuses on communication between the objects and the relationship between them The re lationship between objects is not shown at all in a sequence diagram Sequence dia grams are used throughout the design phase in the development process to show the different scenarios in the system They are suitable in real time spec
51. nd document the different components of a software system before the implementation UML is used to make blueprints of a software system this is necessary within big projects to get an overview of the system UML has a tight mapping to object oriented lan guages and is best suited for designing systems of this kind but UML can also be used advantageous with other programming languages Rumbaugh et al 2001 Though UML is intentionally process independent the authors of UML advocate that UML is used in use case driven architecture centric iterative and incremen tal development processes Rumbaugh et al 1997b Two examples of such pro cesses that are used for development in software engineering are the Unified Pro cess and RUP Rational Unified Process Phillips 1998 Static view Dynamic view Class diagrams State chart diagrams Object diagrams Activity diagrams Use case diagrams Sequence diagrams Component diagrams Collaboration diagrams Deployment diagrams Table 2 1 The nine diagrams in UML version 1 5 belonging to the static view and the dynamic view respectively 4 Chapter 2 UML 2 1 Diagrams in UML The UML is composed of nine different diagrams Which diagram to use de pends upon each special situation and the types of problems being solved Usually the different diagrams are divided into two groups static and dynamic models see table 2 1 The static models also called the structural models und
52. nd easy to use 6 2 2 Return Messages When a user adds a message to a sequence diagram the message will automatically get a return message An exception to this is if the message goes to and from the same object Then the message will not get a return message If the type of the return message is known it will be added to the return message for example if the type of the return value is int the return message will get the label int The return message is placed under the message it belongs to with a distance around one cm If the user wants to hide the return messages he or she can do this in the menu under option Return messages can be switched on and off during the development of a sequence diagram 6 2 Design 31 6 2 3 Sequences Beginners to programming often write sequential programs and because of this one functionality that should be implemented was the opportunity to have messages in a sequence in a sequence diagram If messages are added to a sequence they are automatically arranged and the distance between them and their return messages is updated This leads to a sequence diagram that is symmetric and easy to read If the user on the other hand wants to draw a sequence diagram not having the messages in a sequence this is also possible To illustrate how this functionality has been implemented an example is used If message A is to be added to an already existing sequence after message B mes sage A s start point is pla
53. ner to find and to use new knowledge to solve the given problem This type of education is also called learner centered education since it involves the students more in the learning process and make them more active It seems that 22 Chapter 4 Teaching and Learning Object Oriented Programming people learn best when absorbed in the subject and actively participating in the pro cess towards their own learning and understanding Harley et al 1998 Though this technique with active learning seems to give the learners good understanding quickly it cannot be backed with any statistical data Smialek 2000 It has also been shown that if students work in pairs or in groups better results are achieved This depends on two things The first thing is that students working in a group can solve more complex and interesting problems than a student working alone leading to more active and engaged students The second thing is that students in a group have to discuss for example different designs and argue with each other and this is the kind of reflection that leads to learning Harley et al 1998 One often used technique is pair programming This technique is used both for beginners to programming and for experienced programmers The proponents of pair programming mean that by always being two persons common and un necessary errors can easily be avoided the solutions often get better and the two programmers can switch places to avoid having a per
54. nnen 4 A class diagram 2 o o ee ee 5 A sequence diagram e e 6 A collaboration diagram o o e e 6 Notations for a sequence diagram 11 More notations of a sequence diagram 12 Object constraint language in a sequence diagram 13 The window of the editor o o o 28 The window of BlueJ o 29 Description of the XML file 32 An example of a simple sequence diagram 33 A class diagram describing the system 35 The state machine of a destroy symbol 37 A view of the editota oca ew sarre ia o e 49 Step one in the tutorial o o 51 Step two in the tutorial oo nn 52 Step three in the tutorial 0 o 53 Step four in the tutorial o o 54 Class Ch ser 2 2 a GO Ae ee A a ea 55 Method chooser 2 2 2 2 Connor 56 Window for writing notes 2 o nennen 56 Filename chooser sor 2 0 2 000000 pee o 57 vii Introduction 1 1 Background Today object orientation is widely used both in education and software devel opment Even though object orientation has been taught for quite a long time now there exist many theories how to best teach object oriented programming and thinking to students The widely usage of object orienta
55. ods Since BlueJ is mostly used by begin ners this is a positive thing because the sequence diagrams are only going to reflect implemented classes and methods This functionality also has its drawbacks which will be further discussed in section 6 4 A sequence diagram can be very complex and contain a huge amount of infor mation if all of the notational possibilities are used Since BlueJ and the sequence diagram editor will be used by beginners the sequence diagrams drawn in the ed itor will be of the basic kind The editor does not offer all notational possibilities but only provide the most basic concepts Belonging to the basics of a sequence diagram are objects and actors destroy symbols messages return messages and 27 28 Chapter 6 A Sequence Diagram Editor for BlueJ lifelines Of course this is a big limitation but when beginners draw sequence di agrams these notations are mostly only used Since the editor must not be too complex and difficult to use this subset of all notational possibilities will probably be enough The sequence diagrams that are drawn should also be able to be saved and opened later on There were no special requirements how the sequence diagrams should be saved and in what form Though it seemed natural that sequence dia grams belonging to a certain project should be saved in the same directory as the project it belongs to 6 2 Design 6 2 1 The Graphical User Interface The first thing that I star
56. oftware 2001 Sequence diagrams and scenarios will be described in section 2 3 and in sec tion 2 4 2 2 UML Diagrams in Education 7 2 1 5 Behaviour Diagrams Objects can have different behaviour and states depending on their current actions or conditions There are two diagrams to describe the behaviour and states of an object statechart diagrams and activity diagrams A statechart diagram displays the possible states for an object and the transi tions that will change the state of the object The activity diagram instead focuses on the activities in a special process and the flow of activities It shows how the different activities depend on each other Even though the two different types of behavioural diagrams are closely related an activity diagram can be described as a flowchart showing the flow of activities in a process the statechart diagram concentrates on the object and its different states in a process and what causes the change in state for the object 2 1 6 Implementation Diagrams There are two kinds of implementation diagrams in UML the component diagram and the deployment diagram These diagrams display the view of implementation and the run time implementation structure Booch et al 1999 The component diagram describes the organization of physical software components including source code run time code and executables The deployment diagram depicts the physical resources in a system including nodes co
57. ombine them into a program solving a given task Structures How we learn new things according to special schemas and or plans Learning about these things can simplify the learning and understanding of e g anew programming language Pragmatics Meaning to develop and exercise the skills of planning developing testing debugging and so on 3 1 Programming and Problem Solving One common misunderstanding with programming and software developing is the importance of good problem solving A good programmer is not just an expert at writing code but is also often a good problem solver which results in well written and effective implementations for different problems A given problem can of course be solved and implemented in a number of ways and here the prob lem solving phase is crucial Solving different problems and finding solutions are something that can be exercised The hard part is often to see the whole picture of the problem understand it and find a good solution to the problem One good start is to split the problem into smaller parts So instead of having one big prob lem there are many smaller problems Then these small problems can be solved and by combining their solutions the big problem can be solved This division of a problem into smaller parts is something that must be practiced By doing this repeatedly a person can learn good ways to divide a problem and be able to see common patterns and often old solutions can be reused
58. osing to add a new message to the diagram see A 1 Mark the start for the message on the lifeline of the actor Secretary Then click with the right mouse button and the editor will ask if Do you want to create a new object with this message Answering yes will create a new object First choose which class the object should be created from and then write the name of the object see figure A 6 The sequence diagram will now look as in figure A 2 Sequence Diagram Editor A Secratary new Studernd newSludent Student Figure A 2 The actor and the new student have been added to the sequence diagram 52 Chapter A User Manual Next step will be that the Secretary sets the address of the new student This is done by making a call to the method setAddress which the student has inherited from its super class Person The message call is made by first choosing to add a new message First click on the lifeline of the actor who will make the method call then click on the lifeline of the student to which the call is made Then choose which method to use in the drop down list and click OK The diagram will now look as in figure A 3 When a message is added to a sequence diagram the default in the editor is that the message gets a return message If the type of the return value is known it will be added to the return message Return messages can be switched on and off in the menu under option show return mes
59. ot the case and one of his explanations is that many teachers have a background from programming with procedural languages Another argu ment in the discussion is the use of Hello world programs for beginners Many claim that this is a very bad example to start with and that it is not object oriented at all K lling and Rosenberg 2001 when others mean that if it is correctly used and explained itisa good example Lewis 2000 Ralph Westfall Westfall 2001 says that the Hello World program must be rewritten to be object oriented and gives an example of this He says that in most books for teaching Java the following code is presented class HelloWorld public static void main String args System out println hello world He means that this code will only confuse the students and not teach them anything about object orientation Ralph Westfall says that the code has to be rewritten to include a user created object The result would then be 4 3 Active Learning 21 class HelloWorld public static void printHello System out println hello world class UseHello public static void main String args HelloWorld myHello new HelloWorld myHello printHello The main method in Java is also considered to be a problem by many teach ers since its only purpose is to connect the application to the operating system The code does not naturally relate with any
60. pected that there will be misunder standings in the discussion since everything is new for the members of the group Drawing pictures e g sequence diagrams will then increase the understanding within the group and probably result in a better design of the system since every one in the group can participate in the design A Sequence Diagram Editor for BlueJ The main task with this work was to design and implement an editor for sequence diagrams The editor should work as a plugin for BlueJ BlueJ is an IDE Inte grated Development Environment for Java and is created to be used by begin ners More information about BlueJ and available downloads can be found at www bluej org 6 1 Requirements There were no specific written requirements for this sequence diagram editor The editor should be implemented in Java and designed as a plugin for BlueJ In BlueJ different classes are saved together as projects It seemed quite natu ral that a sequence diagram should be connected to a project meaning that the se quence diagram describes the classes and methods belonging to the given project Each project in BlueJ should also be able to contain an arbitrary number of se quence diagrams When drawing a sequence diagram the user should be able to choose from the implemented classes and their methods In this way the user can not invent own classes and methods that do not exist and are forced to only use existing implemented classes and meth
61. r B and Strong D 2002 The object oriented paradigm More natural or less familiar In Consortium for Computing Sciences in Colleges Nordstr m and B rstler 2002 Nordstr m M and Borstler J 2002 Objektori enterad analys och design med crc kort version 3 0 Technical Report UMINF 02 19 Ume University Department of Computing Science Phillips 1998 Phillips 1998 Rational Unified Process Addison Wesley Pub lishing Company Robins et al 2003 Robins A Rountree J and Rountree N 2003 Learn ing and teaching programming A review and discussion Computer Science Education 13 137 172 Rumbaugh et al 1997a Rumbaugh J Booch G and Jacobson I 1997a UML Notation Guide version 1 1 Object Modeling Group Rumbaugh et al 1997b Rumbaugh J Booch G and Jacobson I 1997b UML Summary version 1 1 Object Modeling Group REFERENCES 47 Rumbaugh et al 2001 Rumbaugh J Booch G and Jacobson I 2001 OMG Unified Modeling Language Specification Object Modeling Group Sebesta 1999 Sebesta R W 1999 Concepts of programming languages Ad dison Wesley Longman Inc Smialek 2000 Smialek M 2000 Teaching ooad with active lectures and brainstorms In Object Oriented Programming Systems Languages and Ap plications 2000 workshop Software 2001 Software C 2001 Object modeling with uml Webpage PDF file http www omg org news meeting workshops pre
62. r an object is added to the drawing area by the user it always gets a lifeline with a default length If the user wants to make any changes to an already added actor or object he or she can click with the right mouse button on the object Then a menu appears and the user can choose between changing the name deleting it and adding a destroy symbol In BlueJ the name for an object can be changed if the user double clicks on the object Because the editor should be similar to BlueJ this function also exists in the program The name of an object an actor or a message can be changed by double clicking on it When a message is added to the sequence diagram the user first marks the starting object with the mouse by clicking on its lifeline Then the message gets visible and follows the mouse like a rubber band effect until the user has chosen the end object of the message This is also done by clicking on the end object s lifeline Most parts in the drawn sequence diagram can be moved after they have been added When a part is marked clicked on it is drawn in red and there appears handles that the user can grab and move the selected part of the diagram The user moves the selected part by pressing the left mouse button and draw the part with the mouse I have chosen this method because many drawing programs use this method press and drag when the user should move for example an object So many users will find this method natural a
63. s which have both attributes and be haviours Though this theory would lead to beginners preferring object oriented thinking some people point out that beginners prefer the procedural way Neubauer and Strong write that the explanation for this could be that students from the first day in school learn mathematics in a procedural way looking at procedural pro cesses applied to data Object orientation has a drawback as many students see it it includes a lot of design and abstraction Most students are not really in terested in design and think of programming as equal to writing code Another disadvantage with object orientation is that many find it more difficult to debug and correct an object oriented system than a system written in a procedural lan guage Neubauer and Strong 2002 Though there are many pros and cons about object orientation almost all uni versities today use an object oriented language in the first programming course and the ones not doing so are planning to This change in programming language has led to discussions about how to best teach object oriented programming and which pedagogy is the best Some mean that since object orientation is quite new in education there are yet no good software tools and teaching support materials This has led to teachers finding it more difficult to teach object oriented thinking 19 20 Chapter 4 Teaching and Learning Object Oriented Programming than the procedural approach K llin
64. sages This could be done any time during the development of the diagram If a message has been added to a sequence diagram and the position of it is not satisfactory the message can be moved This is done by selecting the message by clicking on it and then click on the handle of the message and hold the left mouse button down and drag the message to the right position Sequence Diagram Editor tutorial sd A Sacresany new Studank er Student REDET OTDERRHIFPTHHTFTTTT TER Ff Figure A 3 The actor and the new student have been added to the sequence diagram The actor calls the method setAddress to let the student set its address LA little square that will appear when the message has been selected A 4 A Tutorial Creation of a Sequence Diagram 53 When the method setAddress is called on the student it creates a new object of the class Address and sets its own address This has to be displayed in the sequence diagram by letting the student create a new object of the class Address before returning the method call to setAddress done by the actor This is done by choosing to add a new message Mark the start point of the method call on the lifeline of the student since it is the student creating the new Address To clarify that the new Address is created before the method call to setAddress returns the start point of the message should be placed between the endpoint of the setAddress message
65. same directory as the current project The user then only gets to choose the name of the file If the program 1s not in BlueJ mode the user gets to choose both the name of the file and which directory the file should be saved in All sequence diagrams are saved with the extension sd If the user does not add this to the filename the extension is added by the program When the user chooses to open a file the program only shows files with the extension sd If the editor is in BlueJ mode the sd files belonging to the current project is shown and otherwise the sd files 1s shown in the current working directory Like most programs the editor always asks the user if he or she wants to save the current open sequence diagram if the sequence diagram is being closed for some reason If the user switches BlueJ mode with an open sequence diagram the editor closes the open sequence diagram before changing mode Doing so the editor makes sure that a sequence diagram belonging to a given project is not changed without confirming the correctness with the project 6 2 7 Automatic Consistency Check against BlueJ When the editor is in BlueJ mode a sequence diagram can only include classes and methods already implemented in the current open project If the user draws a sequence diagram belonging to a certain project this sequence diagram has to be checked against this project when it is later opened again If the editor discovers that a class included in the sequenc
66. sentations eai 200 1 tuturial_monday tockey_tuturial l Intro pdf last checked 040302 Westfall 2001 Westfall R 2001 Hello world considered harmful Commu nications of the ACM 44 No 10 129 130 Williams and Kessler 2003 Williams L A and Kessler R R 2003 Exper imenting with industry s pair programming model in the computer science classroom Technical report North Carolina State University and University of Utah http www pairprogramming com csed pdf User Manual In this user manual it is described how the editor works and how to use it The manual contains both a tutorial and sections about each functionality After a short introduction the tutorial follows After this each functionality of the editor is de scribed and explained in more detail Menu File amp Option Seguen ran Editor b Help He Upan LE Add an Actor Add an Object apes Add a Message meer Notes about this diagram Figure A 1 A view of the editor with descriptions for the most important functions 49 50 Chapter A User Manual A 1 Introduction This appendix will help the user to install and use the sequence diagram editor Since the BlueJ program is a project still under development the plugin will only work together with the version 1 3 0 or later versions To be able to run BlueJ and the plugin you will also need JDK version 1 4 2 or later installed on your computer
67. son doing the same thing for a long time Jensen 2003 When beginners use pair programming more com plex and interesting problems can be solved and the student not typing can check for errors in the code which are often easier to discover when sitting on the side Williams and Kessler 2003 It has also shown that when students work ing together the process of learning a new programming language is significantly faster then for a student working alone Williams and Kessler 2003 According to these new approaches for education of object oriented thinking there are some basic elements that are widely used Two of them are use cases and CRC cards Using these methods together with the philosophy of active learning the best result is achieved when teaching object oriented thinking Smialek 2000 Use case session In a use case session the different use cases of the system are modelled and for each use case when it is possible a number of scenarios are developed The participants of the session which the students are write down the scenarios using a very elementary grammar Sometimes these use case sessions can be formed like interviews where somebody plays the role of the user somebody the role of the analysts and the rest of the group review the session by documenting the scenario This documentation is for example done with a sequence diagram or a simplification of one Smialek 2000 CRC sessions CRC cards characterise objects by C
68. tail In chapter five the use of sequence diagrams in education is talked about and advantages and disadvantages are pointed out Next chapter chapter six describes the design and development of the editor for sequence diagrams The editor is described and the design choices are ex plained The system of the editor is also shortly explained and shown After this a chapter follows containing a short summary and conclusions of this work At the end of this thesis an appendix is attached containing an user manual for the editor The user manual helps the user to install and use the editor In BlueJ implemented classes belonging to the same system are saved together as projects UML The development of the Unified Modeling Language UML began in October of 1994 and is an evolution from Booch method by Grady Booch OMT Object Mod eling Technique by James Rumbaugh OOSE Object Oriented Software Engi neering by Ivar Jacobson and other object oriented methods Mrozek et al 2002 In October of 1995 UML 0 8 then called the Unified Method came UML 1 1 was released in September of 1997 and the development is still in progress UML 2 0 was released in 2003 and newer versions are expected soon Bj rkander 2003 UML is a visual modeling language consisting of nine diagrams A model of a software system can be explained as an abstract representation ofthe system These nine diagrams in UML are used to visualize specify construct a
69. ted with was the Graphical User Interface GUI The main thing was that it should be easy and intuitive to use and not differ from the GUI of BlueJ too much see figures 6 1 and 6 2 Since they are beginners who will use the editor it should not include too much functionality and the program should not take a long time to understand and learn The window of the editor contains a drawing area where the sequence diagram is drawn some menus in the top of the window and some icons that are used to draw the sequence diagram The icons represent an actor an object a message and notes for the diagram The GUI is implemented using Java s swing library see http java sun com Sequence Diagram Editor Figure 6 1 The window of the sequence diagram editor 6 2 Design 29 E BlueJ shapes Project Edit Tools View New Class gt Compile Figure 6 2 The window of BlueJ The menu The menu contains three different items file option and help The menu item help has been placed to the right in the window The reason for this is because BlueJ has the menu item help placed here Then the user will quickly find the help if he or she is used to BlueJ To the left in the window file and option are placed In the menu item option the user can choose BlueJ mode on or off and whether to show return messages or not Under the menu item file is open save save as close and quit These menu items are
70. tion in education have raised a lot of questions Is it more natural for a student to think in an object oriented way then in a procedural way Neubauer and Strong 2002 Is it harder to teach an object oriented programming language then a procedural pro gramming language What is the correct way to teach object orientation and which method should be used There exist many opinions in this matter and some guidelines when teaching object orientation with Java have been devel oped K lling and Rosenberg 2001 One often used technique is active learning which can shortly be described as having the students more active in the learning process Smialek 2000 Some commonly used techniques are so called CRC ses sions Role play sessions and Use case sessions They let the students act like dif ferent objects in the system by playing scenarios where the system should achieve different tasks Documenting these plays will help the students in designing their systems When teaching object oriented programming languages to beginners such as for example Java new tools are used One example is BlueJ that is an IDE In tegrated Development Environment for Java designed to be used by beginners see www bluej org It is designed to help students understand the foundations of object oriented programming and is not meant to be used by experienced pro grammers When teaching object orientation today sequence diagrams are often used They have sho
71. ubset of UML for beginners For example LeBlanc and Stiller LeBlanc and Stiller 2000 suggest a subset containing the use case diagram the class diagram the object diagram the collaboration diagram and the sequence diagram The activity diagram and the statechart diagram have not been mentioned but they are also used when tutoring beginners Since object diagrams are quite similar to class diagrams a common opinion is that they are not very important for beginners to UML Sequence dia grams and collaboration diagrams contain and display almost the same information so it may be a good idea to use only one of these diagrams According to different empirical studies sequence diagrams are often shown to be easier to learn and read than collaboration diagrams Kutar Britton and Barker Kutar et al 2002 have performed a study that showes that sequence diagrams are better than collabora tion diagrams The study performed both an empirical and a cognitive study of the two diagrams The result of the cognitive study was that sequence diagrams are easier to read and understand then collaboration diagrams The empirical study did not support this theory as much as expected but it did not reject it neither The con clusion of the study was that sequence diagrams are often better than collaboration diagrams though this must be better established with further studies Even though this study shows that sequence diagrams are to prefer there are certainly a numb
72. whole scenario has its lifeline from the top to the bottom of the diagram A sequence diagram can also display conditions branches and loops see fig ure 2 7 A condition is shown by putting the condition e g an if statement en closed in square brackets to the left of the message name To symbolize a loop an asterisk is used before the name of the message If the number of iterations are known this number can be put in square brackets after the asterisk though this is very seldom the case Miller 2001a To present a branch several arrows can start at a single point each with a guard condition If the object sends a message to itself the call arrow just points back to this object making an U turn see figure 2 6 To express conditions branches and loops in a sequence diagram or another 12 Chapter 2 UML firstObject First new secondObject secondObject Second idNumber updatelD destroy Figure 2 6 The notation for creation of an object and the notation for destroying an object The secondObject is first created be the firstObject and then after sending a message back to the firstObject the secondObject is destroyed by the firstObject UML diagram the Object Constraint Language OCL is used OCL is part of the UML and it is a formal language used to express constraints It is not a program ming language but a specification language that uses simple logic for expressing different constraints Rumbaug
73. wn to be very beneficial for beginners to object orientation and are good since they can for example be helpful in the design phase clarify the program flow of the system and be used in the test phase Fowler and Scott 1997 Kutar et al 2002 2 Chapter 1 Introduction 1 2 The Purpose of this Master s Thesis BlueJ does not have any support for drawing sequence diagrams and this paper will describe the development of an editor for sequence diagrams designed as a plugin for BlueJ The editor will be connected to projects in BlueJ and help the students draw sequence diagrams describing their implemented classes and methods The editor is designed just as BlueJ to be used by beginners and it does not provide all possible notations for a sequence diagram but only the most basic parts The editor has been developed with the same philosophy as BlueJ to keep it simple and make it easy to use and understand 1 3 Thesis Outline In the first chapter the UML and its different diagrams are shortly described Later in this chapter use cases scenarios and sequence diagrams are described in more detail and the advantages of using sequence diagrams in education are distin guished In chapter three teaching and learning software development is discussed in general and in the next chapter chapter four teaching and learning object oriented programming is discussed Different methods are illustrated and active learning is described in more de
74. y Check against BlueJ 34 6 2 8 Creation Messages o o 34 6 3 System Description o e e e 35 6 4 FUture Work aa warn A A AAA 38 7 Related Work 39 S Summary and Conclusions 41 Acknowledgements 43 References 45 A User Manual 49 A Introduction a A ee a eee a A 50 A 2 Installation of the Plugin o o 50 A 3 Starting the Plugin o e e 50 A 4 A Tutorial Creation of a Sequence Diagram 51 A 5 Adding Components to a Sequence DiagraM 55 A 5 1 Adding an Actor o o e e 55 A 5 2 Adding an Object o e 55 A 5 3 Adding a Message o 55 A 5 4 Adding a Destroy Symbol 56 A 5 5 Notes about the Sequence Diagram 56 A 5 6 Return Messages o o 57 A 5 7 Creation of a Sequence o a 57 A 6 Save and Open a Sequence Diagram 57 A 7 Moving Deleting and Editing 58 ALTA Objects o a ne da E e 58 AT 2 gt ACtOTS dla id ae 58 ATI Messages aa dt di ia 59 A 74 Destroy Symbol o o 59 ATI Mateline te e bn hed el tet 59 AB KnownBugs o o e 60 List of Figures 2 1 2 2 23 2 4 2 5 2 6 2 7 6 1 6 2 6 3 6 4 6 5 6 6 A l A 2 A 3 A A AS A 6 A 7 A 8 A9 A Use Case diagram So
75. y of the system and only describes what the system should do The students can then concentrate of the behaviour of the system instead of thinking about how the system should achieve certain tasks The interaction diagrams collaboration diagrams and sequence diagrams are quite similar and display almost the same information They show the interaction between objects in a system and describe the communication between them These diagrams have shown to be very useful for students and quite easy and intuitive to learn and understand Both collaboration and sequence diagrams can really help a student to see the program flow of the system and help them understand how the objects work together Often it can be very hard in an object oriented system to find the flow of program especially for beginners in the area since there is seldom an obvious program flow in an object oriented system as it is for example in a system written in a procedural language Fowler and Scott 1997 Sequence diagrams also have a very prominent role in teaching object orienta tion today together with active learning see section 4 3 Active learning can shortly be described as including the students more in the teaching learning process and making them more active in their search for knowledge Many investigations also show that sequence diagrams are found to be very useful both when designing a new system and also when trying to understand an already existing system Se quence di

A Sequence Diagram Editor for BlueJ

Contents

Download Pdf Manuals

Related Search

Related Contents