1. Cognitive Dimensions  Developed by Thomas Green and Alan Blackwell  Enhanced by Marian Petre Marian PetreMarian Petre  Descriptions of aspects, attributes, or ways that a user thinks about a system called dimensions  Discussion tools used to discover the quality of a system

2. Cognitive Dimensions (2)  Originally focused on the task of programming  Motivated with the view that programming is exploratory design –Creation –Comprehension –Modification  The 14 dimensions follow

3. Viscosity  Resistance to change –Fixed mental model  Examples: The name of a variable in a program

4. Visibility  Ability to view components easily  Non-encapsulation  Examples: –Can’t see all of a large program at once –See only the current state and not the path to it

5. Premature Commitment  Constraints on order of operations –Noun/verb –Verb/noun –Syntax of operations  Examples: –Exploring a maze –Declarations required before problem analysis –Which task objects are represented by widgets (defining the set of operators) –Semantics of buttons

6. Hidden Dependency  Invisible causal links  Examples: –class hierarchies –HTML links –spreadsheet cells

7. Role-expressiveness  Visible or inferable roles and purposes with respect to the whole  Uniform vs. distinguishing appearance of objects –Iconic correspondence: literal, logical, or metaphoric similarity –Indexical correspondence: points to certain spatial/temporal region –Symbolic correspondence: appeals to arbitrary law rule or convention

8. Role-expressiveness (2)  Examples:

9. Error-Proneness –paired delimiters –Forward-only clock buttons –Multiple mode systems without indicators

10. Abstraction  Types and availability of abstraction mechanisms  Examples –Quick-dial phone code –Shortcut key –Macros –Kinematical pairs  Screw and nut  Knob  Slider  Cylinder – turns and slides  Sphere – turns and slides in three dimensions

11. Secondary Notation  Extra information in means other than formal syntax  Examples: –Comments in programming languages –Pop-up windows attached to icons

12. Closeness of Mapping  Closeness of representation to domain  Examples:

13. Consistency  Similar semantics are expressed in similar syntactic forms  Examples:

14. Diffuseness  Verbosity of language  Examples: –Fitting on one screen –Length of time or operation sequence to complete action –Detail available (more detail means components are more widely separated)

15. Hard Mental Operations  High demand on cognitive resources  Examples: –Pointers in C –Deeply nested goal structure

16. Provisionality  Degree of commitment to actions or marks  Examples: – “what-if” experiments – “Undo” and “Redo” mechanisms

17. Progressive Evaluation  Work to date can be checked at any time  Examples:

18. Summary 1. Viscosity 2. Visibility 3. Premature commitment 4. Hidden dependency 5. Role expressiveness 6. Error proneness 7. Abstraction 8. Secondary notation 9. Closeness of mapping 10. Consistency 11. Diffuseness 12. Hard mental operations 13. Provisionality 14. Progressive evaluation

19. Example 1  Automated telephone tree –High premature commitment: need to know category of choice –High viscosity: to change a choice, need to hang up and start again –High error proneness: easy to press the wrong button

20. Example 2  Navigating a web page with underlined text –Low visibility: links are indistinguishable from underlined text –Low role expressiveness: purpose of underlined text is uncertain –High error proneness: users think text is a link