1. Usability paradigms and principles
Designing for maximum usability is the goal of design
History of interactive system design provides paradigms/examples for usable designs
Principles of usability are more general means of understanding usability

2. Introduction Concerns
• How can an interactive system be developed to ensure its usability?
• How can the usability of an interactive system be demonstrated or measured?
 Approaches
Paradigms for usability -examples of successful interactive techniques
Principles for usability-theoretically driven from psychological, computational and sociological knowledge

3. Paradigms for Usability
Historical Perspective on Interactive System Design
Time-sharing
40s and 50s – explosive technological growth
60s – need to channel the power
J.C.R. Licklider -one of the leading advocates of research into human centered application of computing technology at ARPA
single computer supporting multiple users instead of batch processing

4. Paradigms (cont’d) Video Display Units
more suitable medium than paper for presenting computer outputs
1962 – Sutherland's Sketchpad: computers for visualizing and manipulating data
Allowed a computer operator to use a computer to create very rapidly sophiscated visual models on a display screen like TV
Visual patterns cd be stored in computer memory & cd be manipulated by a comp’s processor
Sketch pad demonstrated that:
Comps could be used for more than data processing-visualising and manipulating d-nt representations of info since it cd be made to speak a more human language
one person's contribution could drastically change the history of computing

5. Paradigms (cont'd) Programming toolkits
Engelbart at Stanford Research Institute
1963 – use computing technology to complement man's problem solving activity /computer s teaching humans/human learning from computer
Secret to achieving the above was in providing the right toolkit
the right programming toolkit provides building blocks to producing complex interactive systems like carpenters produce beautiful wood work with right tools
His team of programmers developed a set of programming tools they wd require in order to build more complex interactive systems
Their power is that small well understood components can be composed in fixed ways in order to create larger tools

6. Paradigms (cont’d) Personal computing
70s – Papert's LOGO language for simple graphics programming by children
-By typing in phrases like go, turn left, child programmer could teach the turtle to draw circles, squares, et.c
By adapating the prog. Language to a level children cd understand and use, Papert demonstrated a valuable maxim for interactive system develop’t
No matter how powerful a system may be, it’ll be more powerful the easier it is to use
Future of computing in small, powerful machines dedicated to the individual
Kay at Xerox PARC – the Dynabook as the ultimate personal computer

7. Paradigms (cont’d) humans can pursue more than one task at a time
Window systems and the WIMP interface
humans can pursue more than one task at a time
windows used for dialogue partitioning, to "change the topic“
1981 – Xerox Star first commercial windowing system
windows, icons, menus and pointers now familiar interaction mechanisms

8. Paradigms (cont’d) Direct manipulation
1982 – Shneiderman coined he phrase in ref. to the appeal of graphical-based interaction & highlighted following features:
• visibility of objects
• incremental action at the interface with rapid feedback on all actions
• reversibility of actions so that users can explore without fearing severe penalties
• syntactic correctness of all actions so that every action is a legal operation
• replacement of complex command languages with actions to manipulate directly the visible objects hence DM

9. Paradigms (cont’d) Language versus Action
actions do not always speak louder than words in some cases e.g. information retrieval tasks
DM – interface replaces underlying system
language paradigm
interface as mediator / intelligent agent
User issues instructions in natural language
Interface presents instructions for processing & returns results e.g.
Querying British highway code database about speed limits on various roads, other examples???

10. Paradigms (cont'd) Hypertext 1945 – Vannevar Bush and the memex
key to success in managing explosion of information
mid 60s – Nelson describes hypertext as non-linear (interlinked nodes) browsing structure
hypermedia and multimedia for non text data

11. The metaphor
relating computing to other real-world activity is effective teaching technique
• file management on an office desktop
• word processing as typing
• financial analysis on spreadsheets
• virtual reality – user inside the metaphor
Problems
some tasks do not fit into a given metaphor e.g. type writter keyboard has no space bar which computer keyboard has
cultural bias e.g. meaning of a tick and an x

12. Computer Supported Cooperative Work
Multimodality
a mode is a human communication channel
emphasis on simultaneous use of multiple channels for input and output e.g. both audio (beeps), touch (keyboard, mouse..) and visual (screen)
Computer Supported Cooperative Work
CSCW removes bias of single user/single computer system so needs of many users in one product must be met
Can no longer neglect the social aspects
Electronic mail is most prominent success . Others: google docs and dropbox (groupware)

13. Principles to support usability
General principles which can be applied to the design of interactive systems to promote their usability
Learnability
the ease with which new users can begin effective interaction and achieve maximal performance
Flexibility
the multiplicity of ways the user and system exchange information
Robustness
the level of support provided to the user in determining successful achievement and assessment of intended goals
Class work question: (a) Explain the general Principles which can be applied to the design of interactive systems to promote their usability.
(b) Using an example of an interactive system of your choice, explain how each principle given in (a) can be used to make the system usable.
Use Dix etal. HCI 2nd edition pg for reference

14. Principles of learnability
Predictability
determining effect of future actions based on past interaction history
operation visibility-how the availability of operations which can next be performed are shown to the user
e.g. 1,2,4,16,256,...,...(what are the next two numbers
Synthesizability (synthesizing from previous exp. & knowledge to come to right conclusion/decision)
Ability of the user to assess the effect of past operations on the current state
Assessing the effect of past actions and linking them to present tasks
immediate vs. eventual honesty-ability of UI to provide an observable and informative account of such change e.g. when a file is moved from one folder to another, the process and result is observable.
Ask students meanings of the different English words

15. Principles of learnability (cont’d)
Familiarity
how prior knowledge applies to new system. guessability; affordance
e.g. desktop metaphor from the physical office desk work area, computer keyboard from type writer keyboard, what else?
Generalizability
extending specific interaction knowledge to new situations which are similar/related but previously unencountered e.g. multi windowing systems attempt to provide cut/copy/paste operations to all applications in the same way e.g. MS Office suite, MS Visio, web browsers, search engines, etc
Consistency
likeness in input/output behavior arising from similar situations or task objectives e.g. warnings to aircraft crew which are consistently color coded i.e. red for immediate attn, amber for warning & and green for advisory, phone keyboard & functions are consistent across a number of brands.
Very important for web /e-access for non visual users like the blind & other PWDs

16. Principles of flexibility
Dialogue initiative
freedom from system imposed constraints on input dialogue
Maximise the user’s ability to initiate action towards the system and minimize the reverse for greater flexibility
Multithreading
ability of system to support user interaction for more than one task at a time
e.g. web browsing and word processing or Skype conference call
concurrent vs. interleaving; multimodality
Task migratability
Shd be possible of system or user to pass control of a task to the other or shared e.g. spell checking
passing responsibility for task execution between user and system

17. Principles of flexibility (cont’d)
Substitutivity
allowing equivalent values of input and output to be substituted for each other
e.g. allowing input values in both metres or inches. Centigrade and feihrenheight
representation multiplicity; equal opportunity-may not be a clear difference btn input & output e.g. in a drawing program, user may draw a line & request system for its length or specify coordinates and instruct system to draw line
Customizability
modifiability of the user interface by user (adaptability) or system (adaptivity) e.g. Personal facebook page, chat profiles, etc.

18. Principles of robustness
Observability
ability of user to evaluate the internal state of the system from its perceivable representation
browsability; defaults (set defaults where applicable); reachability (ability to move from one state to another); persistence (duration of effect of communication-voice does n’t last long); operation visibility
Recoverability
ability of user to take corrective action once an error has been recognized
reachability; forward/backward recovery; commensurate effort (if difficult to undo an action, then it sh’d have been difficult to do in first place)

19. Principles of robustness (cont’d)
Responsiveness
how the user perceives the rate of communication with the system
Response time (duration to get state changes from system to user).instant/short durations desired e.g. web browsing
Info to user on status if duration if long is necc.
Stability-invariance of duration for identical or similar resources
Task conformance
degree to which system services support all of the user's tasks
task completeness; task adequacy
It has been suggested by HCI experts that consistency be considered a major category of interactive principles on the same level as learnability, flexibility and robustness. Which principles appear in support of consistency? Pg

20. Use Dix etal. HCI 2nd edition pg 162-175 for reference
References
Alan Dix, Janet Finlay, Gregory Abowd & Russell Beale (2004). Human-Computer Interaction. Hillsdale, NJ: Prentice Hall, ISBN (hardback); (paperback) only outside USA (Second Edition) ISBN Chap. 4
Revision question: (a) Explain the general Principles which can be applied to the design of interactive systems to promote their usability
(b) Using an example of an interactive system of your choice, explain how each principle given in (a) can be used to make the system usable.
Use Dix etal. HCI 2nd edition pg for reference