CMPUT 301: Lecture 18 Usability Paradigms and Principles Lecturer: Martin Jagersand Department of Computing Science University of Alberta Notes based on previous courses by Ken Wong, Eleni Stroulia Zach Dodds, Martin Jagersand

2 Lecture notes: Prepare for lectures by reading chapters in Dix according to the course plan (on the course home page) After the lecture the notes are available in (recently the links to my notes have been overwritten from the main page. The main page is in an account the I don’t have access to)

3 Usability Principles Three main categories: –learnability –ease for new users to begin effective interaction and achieve maximal performance –flexibility –multiplicity of ways for the user and system to exchange information –robustness –level of support provided to the user for assessing achievement

4 Learnability Principles affecting learnability: –synthesizability –Access how past operations affect state –predictability – Predict effects of future observations –Familiarity –Affordance, real world metaphor –Generalizability –Consistency –Similar situations -> similar interaction patterns

5 Learnability Synthesizability: –the user can form a mental model of the behavior of the system –important for the user to predict system behavior

6 Learnability Honesty: –related to synthesizability –the user interface provides an observable and informative account of a change in the system state (immediately or eventually) –e.g., file management (direct manipulation versus command line)

7 Learnability Predictability: –avoid surprises (unless you are designing a game) –the user can learn the effect of an action based on what has already happened –user-centered concept, since computers are largely deterministic

8 Learnability Useful heuristics in design: 1.Operation visibility: –related to predictability –the user can discover what operations can be done 2.State dependence Difficult for user to anticipate effects of an operation if it depends on an invisible state Example vi editor: edit or command mode

9 Learnability Familiarity: –the user can exploit existing knowledge in one domain for effective interaction with a new system –metaphors or guessability –e.g., typewriter and word processors –affordances –i.e., appearances suggest behavior –e.g., stop/play buttons

10 Learnability Generalizability: –the user can extend their knowledge of specific behaviors to similar, unencountered situations –e.g., drawing squares and circles –e.g., cut and paste, drag and drop

11 Learnability Consistency: –the likeness in behavior from similar situations –many forms of consistency –within the product –with earlier versions –with standards –with metaphors –with user expectations

12 Flexibility Principles affecting flexibility: –dialog initiative –multi-threading –multi-modality –task migratability –substitutivity –representation multiplicity –equal opportunity –customizability

13 Flexibility Dialog initiative: –system preemptive –system initiates dialog –user responds to requests for information –e.g., alert dialog –user preemptive –user initiates dialog –system responds –more flexible –need to balance both forms of initiative

14 Flexibility Multi-threading (and multi-tasking): –support user interaction pertaining to more than one task at a time –interleaved –direct interaction with a single task at a time –e.g., using multiple windows for overlapping tasks –concurrent –interaction among tasks is “simultaneous” –e.g., working in one window while beep goes off for new in another window

15 Flexibility Multi-modality: –related to multi-threading –the user interface combines channels of communication for input or output –separate –e.g., mouse, keyboard, or speech input to open a window –fused –e.g., mouse + keyboard –e.g., visual error warning with sound

16 Flexibility Task migratability: –the ability to transfer control for executing tasks between the system and the user –manual, semi-automatic, automatic –e.g., spellchecking

17 Flexibility Substitutivity: –allowing equivalent values of input and output to be substituted for each other –e.g., using arithmetic expressions in numeric fields

18 Flexibility Representation multiplicity: –related to substitutivity –providing many ways to render the system state –e.g., graphic image and levels

19 Flexibility Equal opportunity: –related to substitutivity –blurring the distinction between input and output –use output as input –e.g., dimensioned lines, spreadsheets, math equations

20 Flexibility Customizability: –allowing the user interface to be modified by the user or the system –adaptability –user initiated –e.g., write scripts, change looks, etc. –adaptivity –system initiated adjustments (based on its knowledge from observing the user) –e.g., record scripts, etc.

21 Robustness Principles affecting robustness: –observability –browsability –defaults –reachability –persistence –recoverability –commensurate effort –task conformance –responsiveness

22 Robustness Observability: –the user can evaluate the system internal state through its perceivable interface representation –four related principles …

23 Robustness Browsability: –related to observability –the user can explore the current internal system state via the limited view provided at the interface –browsing has no side-effects on the state

24 Robustness Defaults: –related to observability –the user is assisted by default values that suggest an appropriate response –recognition versus recall of what is right –static –defaults do not evolve during the session –dynamic –defaults do evolve (i.e., the system adapts)

25 Robustness Reachability: –related to observability –the user can navigate through the observable system states

26 Robustness Persistence: –related to observability –the duration of the effect of a communication and the ability of the user to exploit that effect –versus transient –e.g., visual versus audio information

27 Robustness Recoverability: –the user can take some corrective action after recognizing an error has occurred –forward error recovery –effect cannot be revoked –fix effect somehow or start over –backward error recovery –effect can be undone

28 Robustness Commensurate effort: –if it is difficult to undo a given effect on the state, then it should have been difficult to do in the first place –e.g., deleting files

29 Robustness Task conformance: –the system supports all the tasks of interest in a way the user understands –requires task analysis

30 Robustness Responsiveness: –the rate of communication between the system and the user –in general, the shorter, the better

31 End What did I learn today? What questions do I still have?