Cognitive dimensions of notations

Cognitive dimensions or cognitive dimensions of notations

Closeness of mapping

How closely does the notation correspond to the problem world?

Consistency

After part of the notation has been learned, how much of the rest can be successfully guessed?

Diffuseness / terseness

How many symbols or how much space does the notation require to produce a certain result or express a meaning?

Error-proneness

To what extent does the notation influence the likelihood of the user making a mistake?

Hard mental operations

How much

semantic

level? Are there places where the user needs to resort to fingers or penciled annotation to keep track of what's happening?

Hidden dependencies

Are dependencies 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 obtain feedback on an incomplete solution?

Role-expressiveness

How obvious is the

role

of each component of the notation in the solution as a whole?

Secondary notation and escape from formalism

Can the notation carry extra information by means not related to syntax, such as layout, color, or other cues?

Viscosity

Are there any inherent barriers to change in the notation? How much effort is required to make a change to a program expressed in the notation?

This dimension can be further classified into the following types:^[5]

• 'Knock-on viscosity' : a change in the code violates internal constraints in the program, whose resolution may violate further internal constraints.
• 'Repetition viscosity' : a single action within the user’s conceptual model requires many, repetitive device actions.
• 'Scope viscosity' : a change in the size of the input data set requires changes to the program structure itself.

Visibility

How readily can required parts of the notation be identified, accessed and made visible?

Other dimensions

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).

User activities

The authors identify four main user activities with interactive artifacts: incrementation [creation], transcription, modification and exploratory 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.

Design maneuvers

A design 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 incorporating style 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 the repetition viscosity present in the need to change the style of each individual item.^{[citation needed]}

See also

• Cognitive walkthrough – another method for evaluating the usability of an interface
• Conway's law
• Deutsch limit – an adage about the number of elements in a visual language
• Homoiconicity – a representation feature of some programming languages
• Shotgun surgery – a development anti-pattern similar to viscosity
• Software visualization
• "The Magical Number Seven, Plus or Minus Two"

References