Formal Grammar and Human Factors Design of an Interactive
Contents
1. 5 old color NULL 6 starting default color 1 NULL 7 shape discrete shape continuous shape text shape 8 discrete shape separate d shape oo connected d shape Separate Discrete Shapes 9 separate d shape select separate d shape describe separate d shape 10 select separate d shape select old d shape select new d shape 11 select old d shape NULL 12 select new d shape select 1 c b shape select h v shape _ 2The shapes selected and described must be the same For example if line is selected then line must be described IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 Switches for Discrete Shapes 13 select 1 c b shape select 1 c b switch Go 1 14 select h v shape select h v switch 15 select 1 c b switch select line select box select circle 16 select h v switch select horizontal select vertical 17 select line undo non line set line 18 undo non line 1 BOX SWITCH DOWN CONTINUOUS SWITCH DOWN HORIZ SWITCH DOWN VERT SWITCH DOWN all ordered combinations of above 19 set line 1 LINE SWITCH UP 20 select box undo non box set box 21 undo non box LINE SWITCH DOWN CONTINUOUS SWITCH DOWN HORIZ SWITCH DOWN VERT SWITCH DOWN all ordered combinations of above 22 set box BOX SWITCH UP 23 select circle undo non circle set circle 24 undo non2. mers doing nonroutine tasks Other kinds of terminal symbols are possible and will be discussed later Terminal symbols are indicated in small capital letters The word NULL means no user action required Words in paren theses are actions which for brevity are eliminated from the rules shown in the Appendix Nonterminal Symbols The nonterminal symbols represent sets of similar actions that can be grouped together and de scribed in the same way e g draw colored shape draw continuous shape Nonterminals are indicated in lower case letters Starting Symbol For both ROBART grammars the start ing symbol for the action language is DRAW PICTURE This represents a high level task to be serne by the user Thus each picture to be created by the action language is analogous to a sentence in English Metasymbols The metasymbols have been assigned the following meanings The symbol means is composed of The symbol means or The symbol has been defined to mean concatenation or is followed by in order Thus a b means a followed by b in that order To in dicate that order is immaterial which it sometimes is we write atb bta We have also introduced a metasymbol to mean simultaneous Rules The rules of the grammar are given in the Appendix In some cases rules with only one nonterminal symbol on the right hand side have been introduced even though this
3. ROBART action languages because it is commonly used for describing other kinds of languages and has several properties that we liked It is relatively compact is easy to manipulate automatically and can describe an infinite language with a finite set of rules It soon became apparent however that a straightforward BNF like notation was not the ultimate choice We wanted a notation that would 1 describe all and only the legal strings for the user and 2 show the structure of the language with as few nearly redundant rules as possible These turned out to be somewhat contradictory require ments unless we introduced the stratagem of semantic restric tions to prevent the generation of illegal strings Without the semantic restriction given in the footnote for rule 9 for example selecting box then describing circle would be a permissible string We could describe all and only the legal strings by a very lengthy grammar which listed each shape and by then redun dantly having a rule for selecting and describing each one But such a description would lose the general structure that most shapes are constructed in similar ways On the other hand we could write a more terse grammar than the one we have presented showing more of the general structure but at the expense of more semantic restrictions For ex ample if we had one general rule saying that any shape had to be selected and described rather than rule 9 for discrete sh
4. circle CONTINUOUS SWITCH DOWN VERT SWITCH DOWN HORIZ SWITCH DOWN all ordered combinations of above 25 set circle set line set box set box set line 26 select horizontal undo non horizontal set horizontal 27 undo non horizontal LINE SWITCH DOWN BOX SWITCH DOWN VERT SWITCH DOWN CONTINUOUS SWITCH DOWN all ordered combinations of above 28 set horizontal HORIZ SWITCH UP 29 select vertical undo non vertical set vertical 30 undo non vert LINE SWITCH DOWN BOX SWITCH DOWN HORIZ SWITCH DOWN CONTINUOUS SWITCH DOWN all ordered com binations of above 31 set vertical VERT SWITCH UP Describing Indicating Position Location etc of Discrete Shapes 32 describe separate d shape describe 1 c b shape describe h v shape 33 describe 1 c b shape initiate 1 c b shape complete 1 c b shape 34 initiate 1 c b shape cursor at start start operation 35 cursor at start line start circle start box start 36 line start cursor at line point 1 37 circle start cursor at circle center 3The shapes undone must be the ones previously set The shapes initiated and completed must be the same REISNER INTERACTIVE GRAPHICS SYSTEM 38 39 40 41 42 43 44 45 46 47 48 49 50 Si 52 53 54 box start 1 cursor at box corner complete 1 c b shape cursor at end end op
5. 3 and 9 respectively With a rank correlation test Spear ati thisi is a perfect correlation The above test involved some uncontrolled factors hard ware specific labels used possible contamination from suc cessive steps icons versus switches etc We were dealing with existing systems rather than with a pure laboratory experiment We therefore supplemented the testing with detailed questionnaires and found that when subjects were asked which version they thought was easier to learn and re member for each of the shapes the results were similar The reason given was the number of switches Likewise when subjects were asked to compare ROBART 1 shapes similar results were obtained the more switches the harder _ Table II shows the subjective data comparing the ROBART 1 and ROBART 2 versions Each shape was judged to be easier in ROBART 2 than the corresponding ROBART 1 shape These results were individually statistically significant sign test each p lt 0 05 Four reasons were given for these pref erences with the number of switches to change being ranked the most important The others were in descending order remembering undo remembering Go and changing the visual field 234 TABLE II NUMBER OF SUBJECTS OF 10 JUDGING THE GIVEN SHAPE EASIER TO LEARN AND REMEMBER IN ROBART 1 oR ROBART 2 No _ DIFFERENCE RESPONSES NOT INCLUDED ROBART 1 ROBART 2 line 1 7 box 0 9 circle 0 10 continuous line 1
6. 7 continuous box 1 7 continuous circle 0 10 cont open box in ROBART 2 Other detailed tests which asked for pairwise comparisons of shapes within each system and for individual rankings of difficulty also were generally in the direction predicted but only some were statistically significant The overall pattern of results suggests that the design deci sions made for selecting shapes in ROBART 2 led to action sequences that were easier to remember than those for RO BART 1 and within ROBART 1 the sequences for some shapes were easier to remember than others e B line was easier than continuous circle Structural Consistency It is almost a truism that consistency of an interface will _ make it easier to use What is less clear however is precisely what we mean by consistency and more importantly how to identify its absence There are many kinds of consistency for example consistency of terminology the same words consistency of response the same actions result in the same response In this section we consider consistency of struc ture With this notion we are trying to capture the idea that tasks or subtasks that are perceived as similar by the user are described by similar sequences of actions For example if the user perceives drawing shapes as one kind of task then the sequence of steps used to draw one kind of shape should be similar to that used to draw any other kind In this case we are dealing not wi
7. Language For brevity only that portion of the description required for the ensuing discussion will be given Readers wishing further detail can request an unpublished user s manual from the author Functions The following shapes can be created with RO BART 1 line rectangle circle horizontal and vertical lines and continuous lines rectangles and circles The continu ous shapes are sequences of lines rectangles or circles which can be drawn free form on the screen by moving the joystick They are frequently used for artistic effects The size and orientation of these continuous shapes can be varied Fig 4 is an example of the use of continuous circles for artistic effect drawn by Musgrave 11 p 253 Two sizes of text exist and can be superimposed on any of the other shapes REISNER INTERACTIVE GRAPHICS SYSTEM When text is superimposed on a colored background it can be either superimposed directly or surrounded by a black area the size of the character box User Actions Drawing a shape in ROBART 1 requires that the shape and color be selected the size and location and orientation if appropriate be indicated and any special pa rameters such as text background also indicated Color and shape selections remain in effect until new selections are made Selecting Colors Colors are selected by moving the cursor controlled by the joystick into the desired color in the paint box area _ Selecting Shapes Se
8. already on the knob would simply keep it there We thus have two n cessary rules in ROBART 1 one for discrete shapes and another for continuous ones The two rules describe different sequences of actions for initiating the two sets of shapes In ROBART 2 one rule suffices for pots discrete and con tinuous shapes initiate shape cursor at start EXECUTE The user positions his cursor then moves his hand to press the EXECUTE key We thus make the following predictions Prediction 6 In ROBART 1 users who have learned how to initiate discrete shapes will erroneously press the START and Go 2 buttons when attempting to initiate continuous shapes Prediction 7 No equivalent unnecessary action will occur in ROBART 2 These predictions were in fact supported In ROBART 1 70 percent of the subjects erroneously pressed START and GO 2 at least once during the test some of them many times ROBART 2 The ROBART 2 decision to have a consistent design repre sented by fewer necessary rules led to a system that was easier to remember overall We would therefore assert for the user population in question that this was a better de sign even though more physical action was required than in ROBART 1 Connecting Horizontal and Vertical Lines Another slightly more complicated example of structural inconsistency is the method for connecting horizontal and vertical lines in RO BART 1 Fig 5 shows the structure for conn
9. be data it does not necessarily provide explanation of the data obtained For example in ROBART 2 we observed that users unnecessarily pressed EXECUTE after selecting colors It was clear on the basis of the formalism that the structure as designed was different from the structure inferred by users i e the designer s model and the user s model disagreed In sum any technology requires analytic tools testable hypotheses based on theoretical constructs and a body of knowledge built on testing such constructs Formal nota tion appears to have potential as one such tool SUMMARY The field of human factors is frequently judged to be lack ing in rigor To counteract this judgment we have shown by means of a concrete example that 1 user actions at a terminal can be described by means of a formal grammatical notation 2 the formalism can be used to make predictions for comparing design alternatives and locating design flaws and 3 the predictions can be empirically tested We have given a complete formal description of the RO BART 1 system and then made predictions on the basis of the formal description of ROBART 1 and matching portions of ROBART 2 We predicted that selecting shapes in RO 238 BART 1 would vary in difficulty that selecting shapes in ROBART 2 would not vary in difficulty and that selecting any ROBART 2 shape would be easier than selecting the same shape in ROBART 1 These predictions were upheld in ob
10. directly which switch do I use In ROBART 2 on the other hand one general rule suffices for all shapes and there is thus no expectation to unlearn viz tule select shape cursor in icon We would therefore suggest that the ROBART 2 design decision was better than the one for ROBART 1 We do so on the assumption that erroneous actions or rules to unlearn are worse for the infrequent naive user trying to learn or re member a system than slightly more physical action The required rule for ROBART 1 was quickly learned how ever The problems in the next example lasted longer Initiating Shapes The user procedure for initiating a dis crete shape for example a line circle or box can be seen starting from rule 34 34 initiate 1 c b shape cursor at start start operation That is the user puts the cursor at some starting position then presses the START and GO 2 buttons rule 44 The exact REISNER INTERACTIVE GRAPHICS SYSTEM knowledge required for starting lines circles and boxes differs and can be found from the appropriate rules To initiate a continuous shape however rule 83 says 83 initiate c shape full know off cursor at c start knob on Thus the user must turn the knob completely off to prevent unwanted painting move the cursor to the position where the painting is to start then turn the knob on This design decision was made to minimize hand action A user with his hand
11. jective testing of immediate memory and in subjective ques tionnaires We also predicted that users would make errors in attempting to initiate continuous shapes using ROBART 1 and would not make mistakes in ROBART 2 These predic tions were also supported in testing Formal description of interactive systems is an analytic tool It makes possible the examination of a design from the human point of view early in the design cycle We can thus compare some aspects of alternative designs and identify some design inconsistencies before a working model is built The method we have presented is a general one Other inter active systems word processors editors etc can be described by means of a formal notation The predictions we made were based on general properties of the formal description and the approach should therefore generalize APPENDIX ROBART 1 Grammar In the following description terminal symbols are indicated in small capital letters nonterminals in lowercase The rules are numbered for convenience of reference No ordering is implied Headings have been inserted to facilitate locating sections of the grammar The resulting sections are to be used as a rough guide only Picture 1 picture colored shape picture colored shape Colors 2 colored shape color shape shape color 3 color new color old color starting default color 4 new color CURSOR IN RED CURSOR IN BLUE CURSOR IN GREEN
12. position MOVE CURSOR NULL complete c shape full knob off Text Shapes 89 90 91 92 93 94 95 96 97 98 99 100 101 text shape select text shape describe text shape select text shape NULL describe text shape select text background select text size describe text typing select text size select text background describe text typing select text background ADDITIVE BLOCKED SWITCH UP ADDITIVE BLOCKED SWITCH DOWN select text size SINGLE DOUBLE SWITCH UP SINGLE DOUBLE SWITCH DOWN describe text typing initiate typing continue typing complete typing initiate typing POSITION CURSOR start operation i continue typing typing action continue typing typing action typing action symbol operation typing control operation symbol operation symbol symbol operation symbol symbol A B Z 112 9 0 12 1 typing control operation 1 SHIFT 111 complete typing NULL l 240 ACKNOWLEDGMENT The author wishes to thank the following for their careful reading and comments on this paper and or an earlier ver sion J L Bennett E D Carlson R Strong J A Sutton D L Weller and R Williams She also wishes to acknowledge the following for many interesting discussions L Barbosa B C Housel F P Palermo and S N Zilles She also wishes to acknowledge the following for their part in design and or development in RO
13. the specific switch selections required The more general rule would be with the word figural standing for 1 c b and continuous combined tule a select figural shape select switch Go 1 There are thus at least two necessary rules for selecting shapes in ROBART 1 rule a and rule 90 ROBART 1 is thus structurally inconsistent Two differ ent sequences of steps are required where one would suffice We would expect the user to make errors because of this in consistency Having learned one rule for selecting shapes not necessarily consciously the user will apply it in circum stances which are not appropriate This is equivalent to the child who has learned the rule verb ed makes past tense and then insists on saying yesterday I goed Because of the structural inconsistency we would predict the following Prediction 4 A user who has learned to select other shapes will expect to select text in the same way and will show pen this expectation by making expectation responses or actions mean the same things in different contexts and Prediction 5 No equivalent responses will occur in RO BART 2 While not formally tested we did observe such expecta tion responses Users who had learned to select other shapes when trying to select text for the first time would extend their hand toward the switchbox look over the switches as if looking for a text switch or ask
14. value of formal description of action languages is discussed as well as other related work DESCRIPTION OF ROBART Background ROBART 1 is an interactive program which runs on RAIN BOW 1 an experimental color display system developed at the Research Division of IBM in San Jose CA ROBART 1 was originally developed by R Williams to debug and demon strate the RAINBOW 1 hardware 1 It was designed from the inside out with primary emphasis being given to ease of constructing the hardware and to ease of programming rather than outside in with primary focus on ease of use The idea itself was imaginative however and the program has been used frequently to create slides for technical presen tations and has also been used to create artistic pictures for journal covers 11 A similar idea was independently con ceived by R Schoup at Xerox 14 ROBART 2 is a program written for RAINBOW 2 a follow on color display system With experience gleaned from RO BART 1 as input the human interface for ROBART 2 was carefully redesigned to improve ease of use The redesign was the result of a collaborative effort between a psychologist 0098 5589 81 0300 0229 00 75 1981 IEEE 230 TV Siti fg a oman Fo COI ca YF i ca G02 Start End Joystick Fig 1 ROBART 1 as seen by user Colors Shapes BeeT 5100 Joystick Fig 2 ROBART 2 as seen by user and a computer scientist The psych
15. BART 1 or ROBART 2 M Breternitz ITA Sao Paulo Brazil A Fan Mills College G M Gid dings G G Langdon F P Palermo D Raimondi R M Revelle D Silberberg MIT D L Weller and R Williams REFERENCES 1 E D Carlson G M Giddings and R Williams Multiple colors and image mixing in graphics terminals in Inform Processing 77 IFIP North Holland 1977 pp 179 182 2 N Chomsky Syntactic Structures The Hague The Nether lands Mouton 1964 3 D W Embley Empirical and formal language design applied to a unified control construct for interactive computing Int J Man Mach Studies vol 10 pp 197 216 Mar 1978 4 J D Foley and V L Wallace The art of natural graphic man machine conversation Proc IEEE vol 62 pp 462 471 Apr 1974 5 J D Foley The structure of interactive command languages in Methodology of Interaction R A Guedj et al Eds North Holland 1980 pp 227 234 6 G G Langdon Jr P Reisner and D Silberberg Robart 2 A stand alone graphics terminal system for color slides IBM Res Rep RJ2871 San Jose CA July 1980 7 H F Ledgard and A Singer Formal definition and design COINS Tech Rep 78 01 Univ Massachusetts Amherst Feb 1978 8 P M Lewis II D J Rosenkranz and R E Stearns Compiler Design Theory Reading MA Addison Wesley 1976 9 T P Moran The command language grammar Int J
16. IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 229 Formal Grammar and Human Factors Design of an Interactive Graphics System PHYLLIS REISNER Abstract Formal grammatical description has not generally been applied in the human factors area which traditionally draws on be havioral science for its methodology This paper illustrates by means of a detailed example how formal grammatical description can be used as a predictive tool to compare alternative designs for ease of use and to identify design choices which could cause users to make mistakes The paper describes the human interface for two versions of an inter active graphics system intended for use by nonprogrammers It pre sents the action languages for the two versions then shows how these user languages can be described in terms of a production rule notation Particular emphasis is given in the notation to actions the user has to learn and remember i e to cognitive factors The paper then pre sents predictions about human performance based on the formal de scription and exploratory results of testing some of the predictions Since the predictions are based on general properties of the formal description the technique should also be applicable to other action languages Index Terms Action languages analytic tools comparison of design alternatives ease of use measurement ease of use prediction formal descriptio
17. Man IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 Mach Studies vol 14 to be published R A Morrison Graphic language translation with a language independent processor in AFIPS Conf Proc Fall Joint Com put Conf vol 31 Washington DC Thompson 1967 pp 723 731 J F Musgrave Experiments in computer aided graphic ex pression JBM Syst J vol 17 no 3 pp 241 259 1978 P Naur Ed Revised report on the algorithmic language AL GOL Commun Ass Comput Mach vol 6 pp 1 17 Jan 1963 P Reisner Use of psychological experimentation as an aid to development of a query language JEEE Trans Software Eng vol SE 3 pp 218 229 May 1977 R G Schoup Towards a unified approach to 2 D picture manipulation ACM SIGGRAPH Comput Graphics vol 11 p 178 Summer 1977 S Siegel Non Parametric Statistics 1956 M D Wang The rule of syntactic complexity as a determiner of comprehensibility J Verbal Learning and Verbal Behavior vol 9 pp 398 404 Aug 1970 10 11 12 13 14 15 New York McGraw Hill 16 Phyllis Reisner received the A B degree in English from Hunter College New York NY in 1955 and the M S and Ph D degrees in information science from Lehigh University Bethlehem PA in 1971 and 1972 respectively After graduating from Hunter College she studied at The Sorbonne Paris France unde
18. apes and rule 68 for continuous ones we would then need a semantic restriction to prevent selecting a discrete shape and describing a continuous one A simple straightforward BNF notation is diay usable now We can write two different forms of grammars a lengthy legal string grammar of possible use in providing feedback to users about incorrect action sequence and a structure re vealing grammar to locate design inconsistencies However in the long run better notational schemes need to be found or devised which reveal both structure and legal strings While some pattern revealing formalism is required and while BNF is an obvious first choice to explore and is clearly useful it may not be the final solution The Value of Formal Description Analytical Tool A major value of a formal ETA of an action language is that of any analytic tool we prefer to analyze a paper and pencil representation of a system rather than waiting until we have a working model Formal analysis will not preclude all behavioral testing but it may give early switches had to be undone _ Explanation of User Errors explained on the basis of a formalism While testing provides 237 warning of some design flaws and simplify making some design choices Precision Another value of a formalism is simply that it forces us to be precise and concise The simple act of de scribing a system even without comparing alternatives can lead to i
19. ecting ordinary lines and for connecting horizontal and vertical lines The rulescorresponding to these trees start with rule 55 Rules not necessary to the exposition have been omitted from the trees The language was designed for similarity at points marked 1 and 2 The rationale was the avoidance of extra work for the user Once the first line has been drawn successive endpoints only need to be indicated However in order for this to be possible the language is inconsistent at points 3 and 4 No interrupt button is used following selection of horizontal line since this would reset an index in the computer program which stores the latest endpoint However users who have learned that selecting shapes generally requires pressing the GO 1 button continue to do so at points 4 and 5 This is not No corresponding erroneous action was observed in 235 connected d shape separate d shape next d shape describe l c b shape select next c b shape select Il c b shape describe next l c b shape initiate complete initiate complete LINE G01 CURSOR START GO CURSOR END GO NULL NULL SWITCH 1 UP 3 a connected d shape separate d shape next d shape describe next h v shape select next h v shape describe h v shape select h v shape initiate complete initiate complete i l i HORIZ CURSOR START GO CURSOR END GO VERT NULL SWITCH SWITCH 2 uP UP 4 5 b F
20. elp Since the methods were consistent howev r the comparisons are meaningful Subjects also made fewer errors in ROBART 2 than RO BART 1 an average of 6 4 and 8 6 respectively out of a max imum of 57 The results did not arise from a few deviant sub jects but were true for most of them Nine of the ten subjects learned ROBART 2 faster than ROBART 1 no matter which IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 system was learned first and nine of the ten also made fewer errors with ROBART 2 than ROBART 1 Nine out of ten is statistically significant with a sign test p lt 0 05 one tailed The single subject in each case who did not do better with ROBART 2 learned ROBART 2 first and one would of course exp ct the first system learned to be harder All subjects said when questioned that they found the SCREEN ROBART easier to learn and remember than the BOX ROBART although one surprisingly preferred the latter She spent more time learning ROBART 1 thus felt she knew it better and she also preferred the switches be cause she felt more in control Other Related Work The notion that user actions at a terminal can be viewed as a language has been clearly expressed in Foley and Wallace 4 and Foley 5 An early suggestion that BNF descrip tion might be used to predict psychological difficulty of user languages query languages can be found in 13 A short but provocat
21. eptember 29 1980 The author is with the IBM Research Laboratory San Jose CA 95193 formed by a user interacting with a terminal The intent of the paper is to show that an action language can be formally described and that the formal description can be used to com pare alternative designs for simplicity and consistency We are particularly concerned in the formal description with cog nitive factors what a user has to learn and remember rather than with physical actions themselves By examining such a formal description rather than waiting for construction of a real physical model as required for behavioral testing we hope to identify some design flaws early in the development cycle The particular system studied ROBART is an experimental interactive color graphics system for creating slides for tech nical presentations It is intended to be used by people with out computer training Two comparable versions of the sys tem exist ROBART 1 and ROBART 2 The two versions have essentially the same function but differ in the the design of the human interface The paper describes relevant portions of the two ROBART versions in some detail It then presents a formal description of the ROBART 1 action language and makes predictions about human performance based on the formal description of ROBART 1 and matching parts of ROBART 2 Then it presents results of exploratory tests of some of the predic tions The potential
22. eration cursor at end line end circle end box end line end CURSOR AT LINE POINT 2 circle end CURSOR AT CIRCUMFERENCE box end CURSOR AT DIAGONAL CORNER start operation START GO 2 end operation END GO 2 describe h v shape initiate h v shape complete h v shape initiate h v shape cursor at h v start start operation cursor at h v start horiz start vert start horiz start CURSOR AT H LINE POINT 1 vert start CURSOR AT V LINE POINT 1 complete h v shape cursor at h v end end operation cursor at h v end horiz end vert end horiz end CURSOR AT H LINE END POINT ON Y AXIS vert end CURSOR AT V LINE END POINT ON X AXIS Connected Shapes 55 56 57 58 22 60 61 62 63 64 65 66 67 connected d shape separate d shape series d shape series d shape next d shape next d shape _ series d shape next d shape next 1 c b shape next h v shape next 1 c b shape select next 1 c b shape describe next 1 c b shape select next 1 c b shape NULL describe next 1 c b shape initiate next 1 c b shape complete next 1 c b shape initiate next 1 c b shape NULL complete next 1 c b shape complete 1 c b shape next h v shape select next h v shape describe next h v shape select next h v shape select h v switch alternate describe next h v shape initiate next h v shape compl
23. ete next h vshape initiate next h v shape 1 NULL complete next h v shape complete h v shape Continuous Shapes 68 69 70 71 12 continuous shape select c shape describe c shape select c shape select old c shape select new c shape select old c shape NULL select new c shape select c switch Go 1 select c switch CONTINUOUS SWITCH UP select 1 c b switch select 1 c b switch CONTINUOUS SWITCH UP 239 Describing Continuous Shapes 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 describe c shape set knob initiate c shape continue c shape complete c shape set knob fix width vary angle fix angle vary width o fix width vary angle WIDTH ANGLE SWITCH DOWN knob on WIDTH ANGLE SWITCH UP fix angle vary width 1 WIDTH ANGLE SWITCH UP t knob on WIDTH ANGLE SWITCH DOWN knob on full knob on partial knob on full knob on ROTATE KNOB FULL CLOCKWISE partial knob on ROTATE KNOB PARTIAL CLOCKWISE knob off full knob off partial knob off full knob off ROTATE KNOB FULL COUNTERCLOCKWISE partial knob off 1 ROTATE KNOB PARTIAL COUNTERCLOCKWISE initiate c shape full knob off cursor at c start knob on cursor at c start POSITION CURSOR continue c shape change knob change cursor position change knob knob on partial knob off NULL change cursor
24. general structure of command language systems He attempts to describe all levels of a system from the conceptual to the physical device level His formalism is an English like notation with predefined primitives e g WHEN IS THE PROMPT FOR THE ACTION FOR THE RESPONSE TO a programming like construction Do loops and production rules He illustrates his concepts with a simple artificial system for managing message files based on a single machine prompt followed by user response l This report was brought to our attention during the review process It is unfortunately brief 5 pages with little detail and no experimental testing However the work is exciting because it reports a major at tempt to use formal methods in design and presents the impressions of well known researchers on the value of this process REISNER INTERACTIVE GRAPHICS SYSTEM interaction He describes a complete user system interaction rather than concentrating on an action language a sequence of user actions Moran modestly claims that his CLG is just a framework with extensions to help in the design process planned for the future While his example is an artificial one thus precluding behavioral tests describing a single one prompt one response type system the work is important in its attempt to fully describe all levels of a system using formal methods Beyond Simple BNF We originally chose a BNF like notation to describe the
25. gs e g sentences in a language Any particular string can then be described by the particular rules involved in producing it The structure of the string can be shown by a tree diagram based on the rules Traditionally a production rule grammar consists of 1 aset of terminal symbols the words in the language 2 a set of nonterminal symbols invented constructs used to show the structure of the language e g noun phrase 3 a starting symbol e g S for sentence 4 the metasymbols and some common meanings for these are and or and is composed of respectively 5 rules constructed from the above e g S noun phrase verb phrase ROBAR T 1 Grammar Terminal Symbols The terminal symbols for a ROBART 1 grammar represent actions the user has to learn and remember e g 232 PUT LINE SWITCH UP ROTATE KNOB PARTIAL CLOCKWISE POSITION CURSOR AT CIRCUMFERENCE We will call these terminal symbols cognitive terminals and the grammar thus described a cognitive grammar The word cognitive means having to do with knowing in a very broad sense and thus includes understanding learning and remembering We have chosen to write a cognitive grammar for ROBART because learning how to use a system and re membering how to use it after a delay will be of primary im portance for the population we are considering nonprogram
26. ig 5 Tree diagrams showing structure for a connected ordinary lines and b connected horizontal and vertical lines Intermediate nodes have been omitted for simplicity catastrophic at point 4 merely an unnecessary action But at point 5 the internal index is reset the lines cannot be con nected and the user is confused This again was informally observed but not tested experimentally A better design would have been to require all lines to be initiated by a positive action positioning the cursor and pressing START GO 2 Again slightly more work for the user would have been better than trying to be efficient with user actions which caused confusion a DISCUSSION Other Kinds of Terminal Symbols In our formalism we have defined the terminal symbols as the actions a user would have to learn and remember cog nitive terminal symbols Other kinds of terminal symbols aimed toward design of other aspects of a system are also possible Thus to study the physical device in use for a par ticular action we would define physical terminal symbols e g switchbox screen To describe where the user was look ing we would define visual terminal symbols and to de scribe pur physical action we would define action terminals for example MOVE JOYSTICK rather than PUT CURSOR AT DIAGONAL CORNER The physical and visual terminals could then be used to ex amine the assignment of function
27. irst line then in dicate the endpoints of successive ones In order for this strategy to hold for horizontal and vertical lines the user should not push the Go 1 button after the HORIZONTAL or VERTICAL switches have been set GO 1 resets an internal parameter thus losing the position of the endpoint Defining Size Location and Orientation of Continuous Shapes Continuous shapes are drawn continuously as the joystick is moved The size and direction are controlled by rotating a knob on top of the joystick A switch set to SIZE or ANGLE determines whether size or direction is controlled by the knob In order that a user will not have to move his hand from the joystick to start and stop his drawing with these shapes turning the knob completely off counterclock wise prevents drawing from occurring 231 ROBART 2 Action Language The ROBART 2 action language is similar in many respects to that of ROBART 1 The method for selecting colors is the same The method for defining size and location of lines circles and rectangles is the same with the exception that a single EXECUTE key on the keyboard replaces the START END and Go 2 buttons One major difference is the method of selecting shapes The switchbox has been replaced by icons on the screen These are selected in basically the same way as colors by dipping the cursor into the appropriate icon There is one icon for each shape rather than the varying number
28. ive note by Ledgard and Singer 7 reports that several different formal notations were used before coding an interactive editor and claims that formal definition should be used during the design process In addition we have been able to locate two instances of somewhat related work Embley 3 studied one particular control construct for pro gramming interactive dialogues for computer aided instruction the KAIL selector His objective was to apply both empirical and formal methods to assist in the design of this new control construct He first compared the proposed KAIL selector experimentally with an ALGOL like construct using a CAI system to measure understandability of the two constructs At this stage design of the KAIL selector was based on ob servation of factors such as levels of nesting and length of code rather than on formal analysis He then examined the semantics not syntax of variations of the KAIL selector it self using a formal notation to help select between them The variants were examined formally not experimentally While this work concentrates on one particular construct rather than an entire language and is concerned with a tra ditional programming language rather than an action language it is important in that it exemplifies the use of both empirical and formal methods to aid in language design Moran 9 presents a formalism he has devised CLG com mand language grammar to show the
29. lecting a shape requires setting the ap propriate switch or switches to the uP on position For all but horizontal and vertical lines it then requires pressing an interrupt button Go 1 on the switchbox to cause the switches to be read by the computer The appropriate switches are Shape Switch Setting line LINE up horizontal line HORIZONTAL up vertical line VERTICAL up rectangle BOX up circle LINE up and BOX up continuous line continuous rect continuous circle CONTINUOUS up and LINE up CONTINUOUS up and BOX up CONTINUOUS up LINE up and BOX up Defining Size Location and Orientation of Lines Circles and Rectangles Two points on the screen suffice to define these shapes The points are indicated by positioning the cursor at the first point simultaneously pressing START and interrupt Go 2 buttons on the switchbox then positioning the cursor at the second point and simultaneously pressing _ END and Go 2 For lines the start and end points are the two ends of the line for circles the center and any point on the circumference and for rectangles any two diagonal corners Connecting Lines In order for the user to create a sequence of connected straight lines the system has been designed so that the endpoint of one line is treated by the computer as the beginning of the next The purpose of this design was to reduce the amount of human effort required Thus to con nect lines the user merely has to draw the f
30. n human factors man machine interface user errors user oriented design INTRODUCTION N BOTH linguistics and computer science formal grammars _ are used to describe languages precisely In linguistics a grammar is used to describe the rules for generating sentences in a natural language These rules are usually assumed to be the ones a native speaker of the language follows implicitly in creating and in understanding sentences 2 In computer sci ence a grammar is used to describe a programming language to a translator e g compiler or a compiler generator The com piler can then be used to translate statements in the program ming language into machine language 8 10 Formal grammatical description has not however been gen erally applied in the human factors area which draws pri marily on behavioral science for its methodology Since human factors methodology rarely includes theoretical de scription or precise prediction based on formal models the field is often considered soft or even ad hoc at least by some practitioners of other disciplines In this paper we illustrate by means of a detailed example how formal description can be used as a tool to aid the design of systems for ease of use We are specifically concerned with action languages for interactive systems the sequences of button presses joystick motions typing actions etc per Manuscript received January 29 1980 revised S
31. ne 0 0 box 4 1 circle 8 0 continuous line _ 2 0 continuous box 6 0 continuous circle 9 1 cont open box in ROBART 2 Prediction 2 Learning and or remembering how to select shapes in ROBART 2 should not vary in difficulty Prediction 3 Learning and or remembering how to select any shape in ROBART 2 should be easier than selecting the corresponding ROBART 1 shape In Prediction 3 we are ignoring the fact that ROBART 1 uses switches and ROBART 2 uses icons We were not able to con trol this difference but tried to discover its importance in the subjective questionnaires Table I shows the number of subjects unable to select a given shape for both ROBART versions The data given in the table for ROBART 1 include the undo and Go 1 steps since we are comparing the entire sequence of steps required for select ing shapes It is interesting to note that the major portion of the errors arose from the switch setting action Data for the switch setting portion alone omitting errors caused by forgetting the Go 1 button or the undo steps were start ing with line in the table 0 3 8 2 5 and 8 respectively It can be seen from Table I that as predicted the ROBART 1 shapes differ in difficulty This result is statistically significant Cochran p lt 0 05 15 Averaging the results for shapes requiring one switch line and rectangle two switches and three we find the order being as expected the averages being 2 5
32. nteresting insights For example only when writing a formal description of ROBART 1 did the author realize that in spite of many reminders to users to turn off the other switches Testable Hypotheses The precision of a formal descaption also helps in formulating clear testable hypotheses about de sign decisions We could quite clearly specify for example that we were testing initiating actions selection actions etc Quantifiable General Intrinsic Properties of Easy to Use Systems The formalism also permits looking for properties of a language such as length of string or number of necessary tules which will apply generally to other action languages A paper by Wang 16 suggests other measures of string complexity in English some of which may be applicable here We would prefer to be able ultimately to identify intrinsic characteristics of a language which make it easy to learn and use rather than rely exclusively on behavioral testing Further more we would like to quantify such characteristics and show their behavioral correlates And we would like automatic methods for locating design flaws We used a quasi automat able technique Automatic Manipulation A formal notation can of course be automatically manipulated Thus it should be possible to construct and examine any desired combination of strings to construct testing materials of known relative difficulty for example User errors can sometimes
33. of switches per shape in ROBART 1 The interrupt button Go 1 is no longer required A second difference between the two versions is the method of starting continuous shapes In ROBART 2 it is necessary to position the cursor and press the EXECUTE key thus requiring the user s hand to be lifted from the joy stick unlike the ROBART 1 design which is more economical of motion A third difference is the method for connecting lines In ROBART 2 it is not possible to connect lines by simply indicating successive endpoints Both the start and endpoints of all lines must be indicated The functions available are almost identical ROBART 1 has continuous circles where ROBART 2 has continuous open rectangles In the testing to be described later we will treat these as a single comparable shape The effect of these design differences on human perfor mance will be discussed in later sections As with ROBART 1 we have not presented a complete discussion of the ROBART 2 action language Readers desiring further information can re quest an unpublished user s manual from the author FORMAL DESCRIPTION To describe the ROBART 1 action language we will use a production rule grammar This form of description is familiar to linguists and commonly associated with Chomsky 2 It is also familiar to computer scientists as Backus Naur form or BNF 12 A production rule grammar describes a language as a set of rules for describing correct strin
34. ologist the author re designed the user interface and the computer scientist G G Langdon redesigned the internal program structure 6 The formal description was not used in the design of ROBART 2 General Description Both ROBART versions permit a user to create colored shapes lines rectangles circles etc of any size and position and to type in color on a TV monitor The two versions are illustrated in Figs 1 and 2 and a picture created with RO BART 2 in Fig 3 ROBART 1 consists of a TV monitor with a color paint box menu of colors displayed on it a joystick for con trolling the position of a cursor on the monitor a switchbox IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 Fig 3 Picture created by ROBART 2 Menu of colors and icons shown below Fig 4 Graphic art created with ROBART 1 using continuous circle function for selecting shapes and for other control functions and a keyboard for entering text ROBART 1 runs on an IBM System 7 computer and a RAMTEK display processor ROBART 2 also has a paintbox displayed on a TV monitor and a joystick for control of a cursor It runs on an IBM 5100 computer which provides the keyboard and a Genisco display processor The switchbox for selecting shapes in ROBART 1 has been replaced in ROBART 2 by a menu of icons symbolic pictures on the monitor The paintbox and menu of icons can be seen in Fig 3 ROBART 1 Action
35. r a French Government grant and a Fulbright Travel grant In 1960 she joined the IBM Re search Division and is currently at the IBM Research Laboratory San Jose CA Her re search interests focus on human factors of man machine systems particularly development of techniques for improving design of user languages Dr Reisner is a member of the Association for Computing Machinery the American Psychological Association and the Human Factors Society
36. sked to demonstrate the tasks using the same list Testing time was roughly 30 to 40 min on the average for each group A maximum time per item 2 min was set to preclude ex cessive trial and error Success or failure on each item was noted and the kinds of errors observed and classified Al though not of primary interest for testing the predictions overall learning times were also noted In addition the objective test was supplemented by struc tured questionnaires which asked for comparative judgments about specific features of each language comparisons of fea tures between the two languages overall preferences and rea sons for the preferences USING THE FORMALISM TO COMPARE DESIGN ALTERNATIVES Three aspects of the formalism are particularly useful for comparing design decisions 1 the number of different termi nal symbols 2 the lengths of the terminal strings for par ticular tasks and 3 the number of rules necessary to describe the structure of some set of terminal strings The first repre REISNER INTERACTIVE GRAPHICS SYSTEM sents the total number of different action steps in the language the number of words The second represents the number of steps the user has to perform for some given subtask the sentence lengths The third represents the consistency or lack of it in the steps required for a set of related subtasks the number of different sentence types to say similar things We will refer
37. tches the undo step and also the Go 1 step rule 13 must be added Notice that we distinguish be tween selecting a shape selecting a switch and setting a switch Selecting a shape includes selecting the appropriate switch or switches and pressing the Go 1 button as in rule 13 in the Appendix for example Selecting a switch in turn in cludes setting any previously chosen switches to the off posi tion undo ing the unwanted switches then setting the wanted switch to the on position An example of this is rule 17 in the Appendix Setting a switch is the final action of putting the switch in the up position as in rule 19 While the lengths of the terminal strings for selecting shapes varies in ROBART 1 in ROBART 2 selecting any of the above six shapes requires only one step dipping the cursor into the appropriate icon e g select line CURSOR IN LINE ICON select circle CURSOR IN CIRCLE ICON select continuous line CURSOR IN C LINE ICON We would therefore expect the following Prediction 1 Learning and or remembering how to select shapes in ROBART 1 should vary in difficulty If all else were equal we would expect the shapes described by the shorter strings to be easier than the longer ones e g line and rectangle easiest continuous circle hardest We also expect the following 233 TABLE I NUMBER OF SUBJECTS OF 10 UNABLE TO SELECT THE GIVEN SHAPE ROBART 1 ROBART 2 li
38. th individual observable actions but with sets of similar actions We represent such sets of similar ac tions with nonterminal symbols in the grammar Sequences of steps that are similar will thus have a similar underlying structure and will derive from the same rules Structural consistency is important from the user point of view be cause there will be fewer kinds of sequences to remember and less chance of using one kind of sequence when another is correct In this section we will present three examples of i increasing complexity of structural in consistency Selecting Text Shapes In ROBART 1 no action is re quired to select text the keyboard is always available This can be seen from rule 90 viz 90 select text shape NULL Since the length of NULL is by convention zero this would IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 appear at first to be the optimal design choice since the string is as short as possible However there are other rules for select ing shapes which enter the picture For example to select an 1 c b shape line circle or box or a continuous shape the rules are 13 select 1 c b shape select 1 c b switch Go 1 71 select new c shape select c switch Go 1 Both require that switches be set Since these rules are of essentially the same form they could be combined into one more general rule and later differentiated for
39. the terms are not permuted as in Rule 2 where either order was possible Other rules follow the same pattern EXPERIMENTATION In the following section we will make predictions about ease of use of the two ROBART versions and give results of some exploratory tests of some of the predictions We call the results exploratory since we had two existing systems to study and it was not possible to control all the factors we wished We did however supplement the objective testing measurements of time and accuracy with probing question naires in an attempt to understand the truth of the matter The testing was as follows Ten office workers from a temporary office agency learned both ROBART versions primarily using the manuals and other tutorial materials available ROBART 2 had on line tutorials for indicating size and location of shapes The ex perimenter supplemented the self teaching when absolutely required being as consistent as possible for the two versions This was done so that the principal test a memory test could be completed in the time available A maximum of two hours per subject was allotted to the self learning phase To struc ture the learning process subjects were given a list of simple tasks to perform e g draw a green line Half the subjects learned ROBART 1 first and half ROBART 2 Subjects were then given an immediate memory test That is the manuals were removed and the subjects were a
40. to hardware One possible metric would be the number of alternations required for the terminal strings under study the more changes in hand or eye position required the more difficult the design Change in hand or eye position is a recurring theme in human factors Using the number of such changes as a possible metric pro 236 vides a method for judging the icon versus switch distinction in the two ROBART versions Action terminal symbols would be of primary interest in describing systems for users doing repetitive tasks while cognitive terminal symbols are more important for the non routine task and the naive user Assumptions We have made a number of assumptions in das design decisions which should be opened up to discussion There are at least three characteristics of a language which influence its ease of use the number of terminal symbols the lengths of the terminal strings and the number of forms of rules Common practice based on sound engineering practice is to minimize the first e g the number of switches occasion ally the second and rarely the third We would assert that all else being equal the order of importance for naive users doing nonroutine tasks is just the reverse Our reason for this assertion is that human memory limita tion is a major problem in systems for naive or infrequent users and rules describe more of system than do strings and strings more than terminal symbols Rules describe se
41. to the last two aspects as string simplicity and structural consistency respectively The design alternatives examined in the experiments in volved these last two aspects After presenting the results of the experimentation we will discuss the relative importance of all three aspects String Simplicity E To illustrate string simplicity we wu concentrate on the actions for selecting shapes Without regard to design common sense would tell us that all shapes should be selected with equal ease in ROBART 1 that the same should be true of ROBART 2 and that it should be just as easy to select a shape in ROBART 1 as in ROBART 2 Examination of the rules in the Appendix however shows us that this may not be the case To select aline in ROBART 1 for example we see from rule 17 that the user must undo reset to the off position any previously selected switches and then set the line switch Ignoring the undo portion for the moment we see from rule 19 that setting line involves putting the line switch up From rule 25 we see that both line and box switches must be set for circle Continuing in the same way for other shapes we see that the lengths of the terminal strings for setting shapes vary with line and rectangle requiring one switch circle con tinuous line and continuous rectangle requiring two and con tinuous circle requiring three For selecting shapes rather than setting swi
42. ts of sequences of actions strings describe single sequences of ac tions and terminals describe single actions Rules and Predictability We have suggested that learning an action language requires learning rules at least unconsciously The intuitive notion that a system should be consistent can be made somewhat more precise by the notion of necessary rules that we intro duced informally above The consistency of some aspects of a design can be tested with pencil and paper before a system has been built by use of prediction tests These would require teaching a subject the actions corresponding to some rule then asking him to guess at another The more predictable a design the easier it should be to learn and remember In fact predictability of a design suitably quantified should be one measure of the goodness of a design i Overall Results of Tests While a study of overall learning time and accuracy was not our major focus the results are of interest in showing that for the same function and differing interface designs measurable differences in user performance can be found On the average subjects spent less time learning ROBART 2 than ROBART 1 51 min and 76 min respectively roughly a 50 percent difference These are not total times required to learn the systems by self teaching since a maximum time was set some subjects did not complete the entire learning process and some required experimenter h
43. un necessarily expands the number of rules This has been done so that the abstract structure common to both ROBART versions can later be shown How to Read The Notation For those readers unfamiliar with BNF notation we present a brief description of how to read the ROBART rules Rule 1 gives a recursive definition which says essentially that a picture consists of either a colored shape or an indefi nite number of colored shapes Since we are writing an ac tion grammar and in fact a cognitive action grammar we could read the above rule more precisely as to know how to create a picture the user has to know how to create either a colored shape or a series of colored shapes _ Rule 2 says that a colored shape consists of either a color followed by a shape or a shape followed by a color Since the IEEE TRANSACTIONS ON SOFTWARE ENGINEERING VOL SE 7 NO 2 MARCH 1981 user can select either the shape first or the color first both parts of the right hand side are required Rule 4 says that a new color is selected by dipping the cursor into one of the colors Small capital letters are used to indi cate actual possible user actions For brevity we have not listed all the colors Rule 7 says that there are inte kinds of shapes discrete continuous and text Rule 9 says that to create a discrete shape the user has to select it and describe it Since the order of the operations in this case must be as given
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