Cognitive dimensions orcognitive dimensions of notations[1][2] are design principles fornotations,user interfaces andprogramming languages, described by researcherThomas R.G. Green[3] and further researched withMarian Petre.[1] The dimensions can be used to evaluate theusability of an existinginformation artifact, or as heuristics to guide the design of a new one, and are useful in Human-Computer Interaction design.[4]
Cognitive dimensions are designed to provide a lightweight approach to analyse the quality of a design, rather than an in-depth, detailed description. They provide a common vocabulary for discussing many factors in notation, UI or programming language design. Also, cognitive dimensions help in exploring the space of possible designs throughdesign maneuvers, changes intended to improve the design along one dimension.
How closely does the notation correspond to theproblem domain world?
Consistency
After part of the notation has beenlearned, how much of the rest can be successfully guessed, either by combining the known elements in new ways or by trying to use new elements with related meanings? For example: if there exist a 'max(list)' operation to find the largest item in a list, the user may guess that 'min(list)' will find the smallest.
Diffuseness / terseness
How manysymbols or how much space does the notation require to produce a certain result or express ameaning?
How muchhard mental processing lies at the notational level, rather than at thesemantic level? Are there places where the user needs to resort to fingers or penciled annotation to keep track of what's happening?
Hidden dependencies
Aredependencies between entities in the notation visible or hidden? Is every dependency indicated in both directions? Does a change in one area of the notation lead to unexpected consequences?
Juxtaposability
Can different parts of the notation be compared side by side at the same time?
Premature commitment
Are there strong constraints on the order in which the user must complete the tasks to use the system?
Are there decisions that must be made before all the necessary information is available? Can those decisions be reversed or corrected later?
Progressive evaluation
How easy is it to evaluate and obtainfeedback on an incomplete solution?
Role-expressiveness
How obvious is therole of each component of the notation in the solution as a whole?
In addition to the above, new dimensions are sometimes proposed in the HCI research field,[6] with different levels of adoption and refinement.
Such candidate dimensions include creative ambiguity (does the notation encourage interpreting several meanings of the same element?), indexing (are there elements to guide finding a specific part?), synopsis ("Gestalt view" of the whole annotated structure) or unevenness (some creation paths are easier than others, which bias the expressed ideas in a developed artifact).
The authors identify four main user activities with interactive artifacts:incrementation [creation],transcription,modification andexploratory design. Each activity is best served by a different trade-off in the usability on each dimension. For example, a high viscosity (resistance to change) is harmful for modification and exploration activities, but less severe for the one-off tasks performed in transcription and incrementation.
Adesign maneuver is a change made by the designer in the notation design, to alter its position within a particular dimension. Dimensions are created to be pairwise independent, so that the design can be altered in one dimension while keeping a second one constant.[citation needed]
But this usually results in a trade-off between dimensions. A modification increasing the usability of the notation in one dimension (while keeping a second one constant) will typically reduce its usability in a third dimension. This reflects an assumption in the framework that there is no perfect interface and that trade-offs are a fundamental part of usability design.
An example of a design maneuver is reducing the viscosity of a notation by adding abstraction mechanisms. This can be done by incorporatingstyle sheets, an abstraction that represent the common styling attributes of items in a document, to a notation where each item in a document has defined its own individual style.[citation needed] After this design maneuver is made, an editor that changes the style sheet will modify all items at once, eliminating therepetition viscosity present in the need to change the style of each individual item.[citation needed]
^Green, Thomas RG (1989). "Cognitive Dimensions of Notations".People and Computers.V:443–460.CiteSeerX10.1.1.128.270.
^A. F. Blackwell, C. Britton, A. Cox, T. R. G. Green, C. Gurr, G. Kadoda, M. S. Kutar, M. Loomes, C. L. Nehaniv, M. Petre, C. Roast, C. Roe, A. Wong, R. M. Young, "Cognitive Dimensions of Notations: Design Tools for Cognitive Technology",Springer Lecture Notes in Computer Science, vol. 2117, 325-341, 2001.doi:10.1007/3-540-44617-6_31
