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1. Press buttonNames i i Lengthl buttonNames laslho S SS 32 Derme ANOT Eo Clo 2 INES S 7 GE BS Module p ShortestPath Graph randomUser s f Do whichButton p i plit1 i Lengthlp 1 The device might have an interactive feature so pressing a button gives help perhaps showing it ina display panel If so it might be defined partly as follows making use of the current state help doWhat_ help state doWhat Users may wish to ask and get answered questions such as I pressed something but I expected such and such what should I have done Thimbleby amp Addison 1996 discuss how to supply answers to such intelligent help questions We can use the help function to generate an entire user manual A short function tells us how to get from one state to another explain i_ j_ Print To get from the device showing stateNames i to showing stateNames j help i j And here is a small part of the manual Specification led design 15 explain start goal To get from the device showing powerl to showing power2 Press time Press power Ideally one would write more sophisticated routines to generate better natural language rather than the simplistic ones demonstrated here In particular straight forward parametrisation of the routines would allow equivalent manuals to be generated in any appropriate language If we developed a typographical style f
2. H W Thimbleby amp P B Ladkin 1995 A Proper Explanation When You Need One in M A R Kirby A J Dix amp J E Finlay eds BCS Conference HCI 95 People and Computers X pp107 118 Cambridge University Press H W Thimbleby amp P B Ladkin 1997 From Logic to Manuals Again IEE Proceedings Software Engineering 144 3 pp185 192 H W Thimbleby amp I H Witten 1993 User Modelling as Machine Identification New Design Methods for HCI in D Hix amp R Hartson eds Advances in Human Computer Interaction IV pp58 86 Ablex H W Thimbleby 1994 Formulating Usability ACM SIGCHI Bulletin 26 2 pp59 64 H W Thimbleby 1997 Design for a Fax Personal Technologies 1 2 pp101 117 S Wolfram 1996 The Mathematica Book 3rd ed Addison Wesley Specification led design 19 Acknowledgements This paper is a summary of collaborative effort The author is grateful to Ann Blandford Paul Cairns Matt Jones Peter Ladkin Gary Marsden and Jan Witten A preliminary version of this paper was presented at the Institution of Electrical Engineers seminar Living life to the full with personal technologies London 3 June 1998 and was published in the seminar digest IEE Digest 98 268 pp4 1 4 9 20 Specification led design
3. 0 numberOfStates numberOfStates Do Module p ShortestPath Graph randomUser i goal designer i If Length p gt 1 p 2 iJ 11 i numberOfStates We should check that this designer knows how to do the task meanFirstPassage designer start goal 2 Evidently the more knowledge the easier the device is to use A graph of difficulty of use against knowledge can be plotted Plone meanFirstPassage x designer 1 x randomUser start goal x O 1 Mxesibaloall xmowledge Coste jp Cost 120 100 80 F 60 F 40 F 20 F i i Knowledge 0 2 0 4 0 6 0 8 1 This shows that as a user learns more about the device the larger x until they know as much about it as the designer x 1 their performance improves In particular if the user doesn t know much where the graph is steep then even a little help can have a dramatic improvement on their performance We don t have enough space to do this sort of graph justice except to point out different device designs which can easily be explored have different shaped curves and hence this approach gives useful insight into design trade offs Many other sorts of analysis are possible See Thimbleby 1994 a general approach and Thimbleby 1997 the analysis of a particular device for further examples Below we shall show that it is possible to generate user manuals from specifications the structure of manuals ca
4. button ought to have been called reset If so note that you can still get to state quickDefrost by pressing reset i e clock first then the quickDefrost button Also we might think that if such a manual is good what would a device look like that this manual was the complete explanation for To find out all we need to do is change the English routine to one that goes back to the device specification and sees what parts of it are used and which are not Specification led design 17 Ol CeWwALces checkUsed s_ actions_ Module i states Range numberOfStates Eora i 1 s states states StateSet states actions itt Scan d actions i amp states NewManual checkUsed neatTable Actions that weren t needed for the manual d stateNames buttonNames Buttons States clock quickDefrost timer1 timer2 powerl power2 clock quickDefrost time timer1 timerl timer2 timer1 clear clock clock clock clock clock clock power clock quickDefrost powerl power2 Actions that weren t needed for the manual We can look closely at the non blank entries in this table these are the parts of the specification that the user manual did not require Amongst other comments the clear button doesn t seem to be helping much Probably Sharp s specification does not say what clear really does it probably
5. clears a numerical timer setting that he wasn t interested in Nevertheless our generating a manual and then automatically going back to the specification has exposed some potential bad design If this sort of manual is a good idea then the clear button as presently defined is a design feature that needs better justification Many other sorts of manuals can be generated too and by creating them using Mathematica or some other such system systematically we can guarantee their correctness We can also use the technique of going back from a good manual to reappraise the specification After all if we have a good user manual then the bits in the specification that aren t apparently needed are immediately suspicious features Elsewhere we discuss how the technical author s editing starting from a correct manual can be effectively managed even as the device specification changes Thimbleby amp Ladkin 1995 It is possible but requires rather a lot of technical detail beyond the scope of this paper to do something similar in Mathematica the output of the manual generation can be written to a notebook where the technical author can freely edit it as a normal Mathematica document and so make the user manual as readable as desired Mathematica allows cells i e manual paragraphs to be tagged using the tags each paragraph can be uniquely identified even though the technical author has edited them Now if the device specification chan
6. state Which is the most popular button With b Map Apply Plus amp statistics buttonNames Position b Max b 1 1 time We will explore alternative designs below and in particular we shall look at the significance of the time button to usability We can ask how well the users of the simulation performed the task The statistics matrix counts button presses in each state we now convert it to a transition matrix each row of it has to be divided by the total number of transitions out of the corresponding state to convert the matrix to a stochastic matrix each row adds to a probability of 1 Specification led design 9 statsMatrix Table 0 numberOfStates numberOfStates Do statsMatrix i stateNames device b i t statistics b i b numberOfButtons i numberOfStates N statsMatrix statsMatrix Map Apply Plus amp statsMatrix 2 TraditionalForm 0 48 0 2 0 32 0 0 0 0 5 0 25 0 25 0 0 0 0 25 0 083 0 0 5 0 17 0 0 5 0 33 0 0 0 0 17 0 5 0 5 0 0 0 0 0 0 1 0 0 0 N meanFirstPassage statsMatrix start goal 2 61 Since this is better than ignorance 120 steps but worse than the designer s optimal it is likely that this user or collection of users sometimes did the required task or almost did it but whatever they did was not as random as knowing nothing We can determine how thoroughly the user interface simulation has been tested perhaps some transitions hav
7. user interface simulation can give empirically based probabilities and we will analyse them below Here we give the definition of the mean first passage time in its most direct form our associated paper gives a full derivation of the relevant formula The mean first passage time represents a user s difficulty with performing a task AOICORONVCOAL iMeiee Ik_ iC _ 8S tabte ie a SS ie 3 SS ee O macis iir oly fi hemetinil matics 4 wermepeint meteieiss One Welole il iniiiloecOiSicences y Id IdentityMatrix numberOfStates meanFirstPassage matrix_ start_ goal_ Inverse Id ZeroRowCol matrix goal One start Here is how the function can be used meanFirstPassage randomUser start goal 120 Thus the expected time to perform the task to get from the start state power1 to the goal state power2 is 120 button presses Of course the Markov model doesn t know how to use the microwave which is why the number seems so high But the designers of devices should know how to use them We now create a designer s matrix which represents optimal use for any task based on the optimal route from the start to the goal states The random user matrix is converted to a Graph type to Specification led design 7 find shortest paths it can be done conveniently and correctly from the randomUser matrix since exactly its non zero elements are device transitions designer Table
8. Here we see an example of Mathematica output secondElement is to be found at position 2 in the example vector And working the other way round the 2 can be used to select the second element of the vector exampleVector 2 secondElement In all cases in this paper Mathematica code precedes the output from running the code The cases where no output is shown are either straight forward definitions or are stated in the text as not being run for example to save space we did not run the Mathematica code to generate the entire user manual Device definition Mathematica shows how easy reusable development is to do By making minor changes to the definitions here other devices can be developed in the same way Here is Jonathan Sharp s definition of his microwave cooker Because we decided to use exactly his definition for reasons given above the function defined above is used frequently to convert between names and numbers had Sharp defined his device directly in terms of state numbers this would not have been necessary Instead we might have defined each button and state as a numerical constant but the approach we have used makes the device definition easier to read and less error prone device Glock Clock clock clocks Glock Clock quickDefrost quickDefrost quickDefrost quickDefrost quickDefrost quickDefrost timerl timerl timer2 timerl timer2 timerl CMOS Fru elbek elbek elbek CO Clay mCiho la
9. Specification led design for interface simulation collecting use data interactive help writing manuals analysis comparing alternative designs etc Wednesday September 30 1998 Harold Thimbleby Middlesex University LONDON N11 2NQ URL http www cs mdx ac uk harold Abstract This paper shows how to combine a substantial part of the product development cycle of interactive devices into a single co ordinated approach Much can be derived automatically from a suitable specification of the interactive device and it can be derived automatically Normal product development has a device specified and built then has its manuals written then it is used and tested At this late stage design problems may be identified but it is now too late usability studies become academic in so far as the particular product is concerned since it is already effectively in production It would be better if the testing and manual writing could rapidly be obtained from the initial specification before any investment has been made in fabrication This paper offers a design approach that achieves this and it shows how the various views of the design can be used help improve each other for instance the automatically generated user manual can be fed back to suggest improvements in the design A microwave cooker is used as areal example However this paper provides full and unabridged details of everything it discusses by using Mathematica as a rapid
10. ate decision we used Sharp s exact definition to try and emphasise the generality of the approach we didn t choose this definition to fit the needs of the paper m Preliminaries Since this paper is the Mathematica definition of everything the paper talks about it has to start with some Mathematica preliminaries This section can be skipped as they say on first reading though it also provides some examples of Mathematica being used to explain the formatting conventions this paper uses A stylistic consequence of this paper also being a Mathematica document is the rather frequent use of backward references in the text to earlier definitions they have to be earlier else they wouldn t work where they are needed We start by loading the standard Mathematica package for combinatorics to load a shortest path function which we will need for calculating the designer s optimal transition matrix and a basic utility routine lt lt DiscreteMath Combinatorica vector_ element_ Position vector element 1 1 The function pronounced such that defined above gives the numerical index into a vector such that the element would be selected It uses the built in function Position which produces a general result which in turn requires the 1 1 subscript Here is how it is used exampleVector firstElement secondElement thirdElement exampleVector secondElement 2 Specification led design
11. e not been tried out by any user so far We could use Mathematica to summarise the as yet untested transitions It may be that by getting users to try these transitions out that we discover some obscure behaviour in the device Perhaps some of the transitions the device supports are counter intuitive The following simplistic code tells us what buttons users have not yet been tried it doesn t try to produce good English DO Lic SicacLscics ilo S SS OW wWieaime MN lxechy Carie co jwess H buttonNames b when in state stateNames s b numberOfButtons s numberOfStates Nobody tried to press clock when in state powerl Nobody tried to press clock when in state power2 Nobody tried to press quickDefrost when in state power2 Nobody tried to press time when in state timer2 Nobody tried to press time when in state powerl Nobody tried to press clear when in state power2 Nobody tried to press power when in state powerl Nobody tried to press power when in state power2 What transitions did the users try but which the device isn t designed to support Specification led design Do If statistics b s m 0 amp amp devicel b s stateNames s Print buttonNames b was pressed in state stateNames s but did nothing b numberOfButtons s numberOfStates clock was pressed in state clock but did nothing quickDefrost was pressed in state quickDefrost but did nothing clear was pressed in state clock but d
12. evice b i 1 b numberOfButtons i numberOfStates The nonTime matrix has zeros where a state transition can only happen by pressing the time button whereas the onlyTime matrix has ones where the time button works Where the onlyTime matrix is 1 the nonTime matrix must be zero Printing the two matrices below makes things clearer Print NU nonTime TraditionalForm Me onlyTime TraditionalForm 0 75 0 25 0 0 0 0 001000 0 5 0 5 0 0 0 0 001000 0 5 0 25 0 0 0 25 0 0003100 0 5 0 25 0 0 0 0 25 001000 0 5 0 25 0 0 0 25 0 0003100 0 5 0 25 0 0 0 0 25 001000 We can then plot the performance of a user whose behaviour is represented by a linear combination of these two matrices Specification led design 13 PILOKE meanFirstPassage 1 k nonTime konlyTime start goal ie 00l s9997 8000 6000 4000 2000 E 0 2 0 4 0 6 0 8 1 We will skip the details but by plotting the graph on a decreasing interval we can find a narrower range of k that gives the best user performance PALO meanFirstPassage 1 k nonTime konlyTime start goal lie 592 Sie Be 39 39 32 39 991 991 991 991 991 595 O 5925 0 593 0 5935 0 594 0 5945 0 595 This is saying that for the given task and other things being equal making the t ime button be used 60 of the time three times more likely than a fair use of 20 will make the dev
13. ges the notebook can be re read and a report automatically made of any cells whose original generated text has changed or is new or has been deleted This report can be automatically interleaved back into the manual so that the technical author could more easily associate the comments with the affected parts of the manual The technical author can also point out peculiar features or ones that are hard to explain Mathematica could then track these suitably flagged comments back to the offending parts of the specification much like we did above for instance the technical author s comments would end up in the specification table instead of the dashes Specification led design m Conclusions The development method described in this paper is very powerful and with a system such as Mathematica it is also very easy to do With Mathematica or with bespoke design packages all the code could be concealed from designers this paper because it is explicit gives an unnecessarily technical feel to the approach The method is not limited to finite state machines as might be supposed Thimbleby amp Ladkin 1997 discuss generating user manuals for quite complex systems such as parts of the A320 fly by wire airplane where we use a logic based approach The Mathematica code shown in this paper will work with other devices by making only the appropriate changes to the device specification This paper then is itself a complete gad
14. get design package everything discussed in this paper is explicitly and fully defined and one is surprised that more devices are not designed in this way rather than by using superficial tools that emphasise looks against specification Mathematica could be accused of being esoteric it does have complexities this paper avoided our further work is using Java to allow the user interface of the development environment to be put on the World Wide Web and for designers anywhere in the world to write Java applets that can be analysed and simulated on the site With world wide use of simulations one would be able to obtain global empirical statistics of device use We also hope to promote good practice in user interface design m References P Cairns M Jones amp H W Thimbleby 1998 Reusable Usability Analysis with Markov Models working paper available from the authors J Sharp 1998 Interaction Design for Electronic Products using Virtual Simulations PhD thesis Brunel University N Stanton ed 1998 Human Factors in Consumer Products Taylor amp Francis H W Thimbleby amp M A Addison 1994 Manuals as Structured Programs in G Cockton S W Draper and G R S Weir eds BCS Conference HCI 94 People and Computers IX pp67 79 Cambridge University Press H W Thimbleby amp M A Addison 1996 Intelligent Adaptive Assistance and Its Automatic Generation Interacting with Computers 8 1 pp51 68
15. ical LED display of green text on a black background by providing options such as FontFamily Courier FontColor RGBColor 0 1 0 Background GrayLevel 0 and its correct dimensions in the definition of the cell In a running Mathematica session pressing the buttons makes this display work as well as collect data on the users behaviour with the simulation Mathematica can itself generate button definitions from any device specification and one can extend the definition to include explicit sizes positions and so forth We will give an example below Thus the user interface itself can be defined by the same device specification This is very important to make the analysis both mathematical and empirical use consistent specifications they can be edited easily and only in one place m Analysis and graph drawing For illustrative purposes we now do a Markov analysis of the device which is a good way of estimating how a user making random errors would perform using the device It should be noted that this approach is a keystroke level model but which allows for errors In particular we will be able to draw a graph of a user s task performance against how accurately how error free or how well they know how to do the task perfectly A working paper available from the author is available to describe the particular benefits and many further details of the approach Cairns Jones amp Thimbleby 1998 Publi
16. ice easier to use In actual design we should consider all possible tasks the device is intended to support and we should attach weights to each task e g quick defrost is less important or done less often than cooking at power level 1 then we could calculate the optimal size relative frequency of use for each button 14 Specification led design m Automatic and hence correct help There is a legal requirement that descriptions of products correspond with the products themselves under the Sale of Goods Act 1979 as amended by the Sale and Supply of Goods Act 1994 and the Sale of Goods Amendment Act 1994 products should be fit for purpose and should correspond with the description of them Thus it is the UK law that user manuals are correct or if we take a weaker view that the manufacturer at least knows what the correct description is so that some appropriate description but truthful can be written for the user Although our device definition is very basic it can be used to generate quite useful help for the user or for technical authors We now define a function help that explains the shortest path the least number of button presses to get from any state to any state The definitions given below can be adapted straight forwardly to provide clearer help if buttons aren t actually pressed maybe they are knobs that have to be twisted WHLCMBCcOMm S E sS Do Iif device i s stateNames f Print
17. id nothing power was pressed in state clock but did nothing power was pressed in state quickDefrost but did nothing More sophisticated analysis would likely use a log of the users button presses whereas the statistics collected in the function press only counted state changes this throws away the information about which button is pressed and it also loses information relating to tasks that take more than one button press m Exploring alternative designs Specification led design is ideal to explore trade offs for alternative designs Obvious alternatives for Jonathan Sharp s device would be to explore designs that have one button per state so buttons change the state of the device predictably or to have a single button that cycles through all states Both of these alternative designs are simple but are only appropriate for a device with a small number of states This section of the paper shows how we can explore some alternative design ideas that would also be appropriate for devices with much larger number of states For clarity we will not introduce new device specifications just different ways of interacting with the original device The mean first passage time says how many button presses a user takes From the graph it is clear that an ignorant user one behaving quite randomly is very inefficient taking 120 button presses to doa task that a knowledgeable user can do in just 2 presses Can we modify the design so that ignora
18. l clock quickDefrost powerl power2 powerl power2 buttonNames clock quickDefrost time clear power stateNames clock quickDefrost timerl timer2 powerl power2 numberOfStates Length stateNames numberOfButtons Length buttonNames The five parts of the device specification here represented by five variables buttonNames numberOfButtons etc can be encapsulated into a single structure and for actual development work this would have been preferable rather than proliferating five variables per design Mathematica provides various ways to do this packages object oriented programming etc but for such a brief paper as this to do so would introduce unnecessary technical detail Sharp didn t write his specification in Mathematica Mathematica can however print the specification above quite closely to the style that Sharp used in fact Mathematica provides an extensible user interface to make the entry of tabular data as easy as using a spreadsheet We define a function neat Table to make a reasonably neat tabular presentation of any device It is probably clear from the intricacy of this code that almost any typographical details can be accommodated Specification led design 3 neatTable title_ device_ stateNames_ buttonNames_ With heading StyleBox FontFamily Helvetica FontSize A 10 FontWeight E Bold amp subHeading StyleBox FontWeight Bold amp S
19. ls allStates Search seq_ Do Module p Append seq b g g StateSet allStates p If Length g 1 amp amp MemberQ goals g 1 explain g 1 pl goals DeleteCases goals g 1 AppendTo queue pj b numberOfButtons Search queue While goals Search First queue queue Rest queue Then by defining some routines to explain things in for instance English we can print out the sequences of button presses to get to each state We now have the user manual that tells a user how to do anything regardless of what the device is doing to start with Notice how short it is perhaps because of its brevity as we shall soon see we can get some interesting design insights straight from it oime Whatever the device is doing you can always get it to Say mistet Sa SS saa VWs Saytisel ts c i s2 s lt gt then USS savinise fe 5 Say MES s_p E E S A S a ES E EE English state_ actions_ Print stateNames state by pressing SayList ToString l oucconemneslactions iy NewManual English Whatever the device is doing you can always get it to clock by pressing clock quickDefrost by pressing quickDefrost timerl by pressing clock then time timer2 by pressing clock time then time powerl by pressing clock time then power power2 by pressing clock time time then power Looking at these instructions it looks like the clock
20. n be analysed without anyone ever having to see them for example to identify the hardest e g most lengthy parts of them and Specification led design then to redesign the device so that awkward parts are simplified Thimbleby amp Addison 1994 show how to use flow analysis arguing that user manual design should follow program design best practice m Looking at empirical statistics of use The statistics of use collected could be used directly in link analysis and with other conventional design techniques Stanton 1998 but we shall continue with the Markov analysis We could use the function neat Table defined above to print out the statistics in a neat form The actual statistics data used to calculate the information in this section is shown below In fact the numbers here were originally printed by asking Mathematica for the value of statistics during a session The Mathematica code below can be run to initialised the variable statistics e g during a live demonstration of this paper SCACUScalLes Ae 4 il i O O 4S 2 1 2p il Of O7 Sp G7 07 O Lh Ep 2y Ar 2p ir Oy WG 1p 2 Uy Oy 0Y neat Table BUECOM presses in each stats statistics stateNames buttonNames Buttons States clock quickDefrost timer1 timer2 power1 power2 clock 2 4 1 1 0 0 quickDefrost 5 2 1 2 1 0 time 8 3 6 0 0 1 clear 4 2 2 2 1 0 power 6 1 2 1 0 0 Button presses in each
21. nt users are more efficient Much of their inefficiency comes about because they press buttons that do nothing Let us modify the design so that users are discouraged from pressing pointless buttons We could imagine that each button can be lit up perhaps so that its name is only visible when its light is on If the device was like a video recorder it would most often be used in the dark anyway so lights on buttons would have a dramatic effect on users behaviour To analyse this new design we construct a new matrix 1itButton that represents the random behaviour of users who only press buttons that do something The matrix can be calculated from the random pressing matrix used above by zeroing the diagonal presses that do not change state and renormalising Specification led design 11 IIc EOM Walole Lic a g wemclomUsec lle Ol i numberOfStates j numberOfStates litButton Table litButton i Plustd 1litButton i i numberOfStates N meanFirstPassage litButton start goal 70 8 This is an improvement on 120 which suggests we should do some empirical experiments with users To do so we can revise the Mathematica simulation and arrange for buttons to change colour depending on whether they actually do anything in the current state We define newInterface to be an expression that Mathematica can render as a row of coloured buttons but for the time being we don t choose any particular colou
22. o be clock Arguably a device definition should specify its initial state the state a device is in as soon as it is used for many devices this state will be its being off state stateNames 1 clock The definitions given in this section merely show the name of the current state in the display It is possible to display anything not just plain text but to do so would take us beyond the scope of this paper 4 Specification led design When a button on the simulation is pressed Mathematica will arrange for the function press to be called with the button as a parameter press theButton_ Module nb ButtonNotebook collectStatistics theButton state state device buttonNames theButton stateNames state NotebookFind nb display All CellTags SelectionMove nb All CellContents NotebookWrite nb Cell ToStringl state After collecting any useful statistics this function uses the device specification to determine the next state The next few lines of the function locate the device s display cell in the current Mathematica notebook Mathematica can have several notebooks that is windows running together which is why the variable nb is required the text displayed in that cell is selected and replaced with the name of the new state By defining collect Statistics we make press collect empirical statistics as the simulation is used For simplicity we will just collect state transi
23. or user manuals then all devices processed would be able to use that style compare this idea with the tabular typesetting of the device specification shown earlier Also one can generate HTML manuals for the World Wide Web and then the user can also follow hypertext links to help understand the workings of the device The entire manual can be printed with the following Mathematica code DOLE w jy amp plaiaji Jll 1 Length stacenanas h j Lengthl stateNames This doesn t provide a particularly easy read certainly not all of it but it is a complete and correct manual that a technical author could work from However for many devices including this microwave cooker a user s tasks won t be so much to get from a known state to another state but simply to get to the desired state regardless of the initial state We will now generate a manual for this sort of use To represent a device in an unknown state we represent its possible states as a set and we define a function to find out what set of states the device will be in after a given sequence of button presses StateSet initialStates_ presses_ If presses initialStates StateSet Union Map stateNames device First presses amp initialStates Rest presses A breadth first search can then be used to look for unique states 16 Specification led design NewManual explain_ Module allStates Range numberOfStates goals queue goa
24. prototyping environment Any similar device can be analysed in the same way directly from the paper E Introduction This paper shows that the definition of a device its simulation its usability analysis and its user manuals in any language and interactive help if required can all be worked on directly and efficiently in a suitable design environment If part of the design process suggests improvements say that the user manual has an obscurity then it can be changed directly by modifying the specification and the new specification will update all other parts of the product the analysis the simulation and so on Importantly the approach only has one definition of the device thus changes as occur during iterative design and product revision immediately and automatically affect all parts of the development process the analysis the simulation the help and even the hardware Specification led design is so efficient that it is effectively concurrent engineering Specification led design 1 The importance of the approach is that many components of a product are derived efficiently and automatically almost at once In normal design methods there is a sequential and costly progression from specification through fabrication to manual writing and finally usage Only at later stages then will many usability problems be identified but by then the product is already fabricated and many of the usability insights would be
25. rs Instead RGBP laces records the slots where the colour specifications are needed so the colours can be updated every time a button is pressed newInterface Cell BoxData RowBox Map ButtonBox ToStringl ButtonFunction 1 newPress ButtonEvaluator Automatic Background RGBColor _ amp buttonNames Active kt True TextAlignment Center FontFamily Courier FontSize 20 FontWeight Bold CellTags newButtons RGBPlaces Position newInterface RGBColor _ The new buttons use a new press function otherwise they d control the user interface simulation shown earlier in this paper The code is much as before except that a loop assigns colours to each button red for buttons that change state and light gray if they do not change state newPress theButton_ Module nb ButtonNotebook state device buttonNames theButton stateNames state NotebookFind nb newButtons All CellTags Do newInterface ReplacePart newInterface If state device fi stateNames state NEBWCOLOL O 9 0 9 O 9 REsColoir il 0 O RGBPlaces i 1 numberOfButtons NotebookWrite nb newInterface NotebookFind nb newDisplay All CellTags SelectionMove nb All CellContents NotebookWrite nb Cell ToStringl state It is possible that the user interface simulation described above has been used which can only happen if this paper is r
26. shed papers further explaining the motivation for such analyses are Thimbleby amp Witten 1993 and Thimbleby 1994 We will analyse the user task of getting from state power1 to state power2 To consider a particular task we do need to know the appropriate state names Alternatively it is possible to analyse all pairs of states hence all tasks the device supports and obtain statistics which would typically be weighted by the relevance or importance of the tasks to users However for the purposes of this paper analysing just one task is sufficient start stateNames powerl goal stateNames power2 We now convert Sharp s definition into a stochastic matrix 6 Specification led design randomUser Table 0 numberOfStates numberOfStates Do randomUser i stateNames device b i t 1 numberOfButtons b numberOfButtons i numberOfStates Here is the matrix displayed in traditional mathematical notation randomUser TraditionalForm 2200 0 2244000 2 1 1 1 z3353 0 55 Zor EES 35 0 55 2 f 1 1 7 rr 9 0 Each row gives the probability that the user will change the state thus if the device is in state 1 the user will change it to state 2 with probability 1 5 ie first row second column This matrix will be used for the analysis The assumption is that each button on the device is pressed with equal probability There are five buttons so all the probabilities are so many fifths The
27. tion counts statistics Table 0 numberOfButtons numberOfStates collectStatistics theButton_ state_ statistics buttonNames theButton stateNames state The following code is the definition of a row of buttons to control the device Cell BoxData RowBox UIE Omens CLOR Y ButtonFunction gt press clock ButtonEvaluator gt Automatic Ue c Oialsions VOibliLel lt Celkeizieestic Y ButtonFunction gt press quickDefrost ButtonEvaluator gt Automatic BUSEOMNBO VW sins ButtonFunction gt press time ButtonEvaluator gt Automatic ButtonBox Clear ButtonFunction gt press clear ButtonEvaluator gt Automatic ButtonBox Power ButtonFunction gt press power ButtonEvaluator gt Automatic Active gt True To use the buttons Mathematica would change the display mode of the definition and show a row by default of actual buttons Specification led design 5 Clock Quick defrost Time Clear Power The device s simulated display is a simple Mathematica cell shown below with an appropriate name so that the press function can locate it In its simplest form it could be just Cell CellTags display If desired Mathematica allows cells and buttons to contain further typographical details such as their font size and colour For example the device s display can easily be made to look more like a typ
28. tyleBox GridBox FrameBoxl GridBox GridBox Transposel Join heading Buttons subHeading i buttonNames ColumnAlignments Right GridBox heading States GridBox Join subHeading l stateNames device ColumnLines True RowLines amp True False ColumnLines True f heading title FontFamilyA Palatino FontSizefA 9 FontWeight Plain DisplayForm neatTable Sharp s Microwave cooker device stateNames buttonNames Buttons States clock quickDefrost timer1 timer2 powerl power2 clock clock clock clock clock clock clock quickDefrost quickDefrost quickDefrost quickDefrost quickDefrost quickDefrost quickDefrost time timer1 timer1 timer2 timer1 timer2 timer clear clock clock clock clock clock clock power clock quickDefrost powerl power2 powerl power2 Sharp s Microwave cooker The table is read as follows choose the column according to the current state of the device then read off the next state of the device from the row corresponding to the button pressed If we hadn t wanted all the typographical details just so Mathematica could have printed the specification in a basic form just with TableForm device m Simulating the user interface To simulate the device we use a global variable to keep track of the changing state of the device as buttons are pressed We will start the device in state 1 which happens t
29. un in a Mathematica session rather than just being read on paper so at this point we don t know what the actual state of the device should be and so we don t know what colour the buttons should be The easiest thing is to press any button manually so the code will update the state and set the button colours correctly 12 Specification led design m 60668 quickDefrost Baie pea power We hope that the highlighting of a button affects whether a button is pressed a button should be pressed only if it is highlighted More generally changing the physical design of the user interface will affect how likely a button is pressed For example if a button is made bigger and has a more attractive appearance it would be used more The question is how would this affect the user s ability to perform tasks To help answer this design question we can use the mean first passage function to work out the expected time of performing a task as a function of the proportion of time a button is used As an example we construct two matrices nonTime which represents a user who never presses the time button and onlyTime which represents a user who only presses the t ime button onlyTime nonTime Table 0 numberOfStates numberOfStates Do If buttonNames b time nonTime i stateNames device b i 1 numberOfButtons 1 b numberOfButtons i numberOfStates Do If buttonNames b time onlyTime i stateNames d
30. very hard to take back to the specification even it was still available For this paper to illustrate our approach we have used the symbolic mathematical system Mathematica Wolfram 1996 Mathematica is sufficiently powerful that everything described in this paper is completely and fully specified here Many popular system development environments especially those aimed at providing visual realism would have been inappropriate because they never explicitly know what the device specification is and none of the automatic benefits discussed here could have been be obtained This paper was developed and printed entirely within Mathematica all the examples are genuine and have not been re keyed or fudged in any way Stylistically this does have the disadvantage for this paper that explaining the method is interleaved with potentially distracting explanation of the Mathematica code If desired the approach could be packaged e g in Java in sucha way that none of the technical details would be visible to a designer However we felt that for the purposes of this paper being able to see that the method works and giving completely open details was more important Not only does this paper claim that specification led design is a useful approach but it provides complete details for anyone to copy the approach As a running example we shall use the definition of a microwave cooker as given in Jonathan Sharp s PhD thesis Sharp 1998 As a deliber

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