Cognitive dimensions or cognitive dimensions of notations are design principles for

notation In linguistics and semiotics, a notation system is a system of graphics or symbols, Character_(symbol), characters and abbreviated Expression (language), expressions, used (for example) in Artistic disciplines, artistic and scientific disciplines ...

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fro ...

s and

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

s, described by researcher Thomas R.G. Green and further researched with Marian Petre. The dimensions can be used to evaluate the

usability Usability can be described as the capacity of a system to provide a condition for its users to perform the tasks safely, effectively, and efficiently while enjoying the experience. In software engineering, usability is the degree to which a softw ...

of an existing ''information artifact'', or as heuristics to guide the design of a new one, and are useful in Human-Computer Interaction design. 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 through ''design maneuvers'', changes intended to improve the design along one dimension.

List of the cognitive dimensions

Thomas Green originally defined 14 cognitive dimensions: ; Abstraction gradient : What are the minimum and maximum levels of abstraction exposed by the notation? Can details be encapsulated? ; Closeness of mapping : How closely does the notation correspond to the problem domain world? ; Consistency : After part of the notation has been learned, 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 many

symbol A symbol is a mark, Sign (semiotics), sign, or word that indicates, signifies, or is understood as representing an idea, physical object, object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen by cr ...

s 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 hard mental processing lies at the notational level, rather than at the

semantic Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...

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 Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

on an incomplete solution? ; Role-expressiveness : How obvious is the

role A role (also rôle or social role) is a set of connected behaviors, rights, obligations, beliefs, and norms as conceptualized by people in a social situation. It is an expected or free or continuously changing behavior and may have a given indi ...

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: :* '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, 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'' reation ''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. 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. 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.

References

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External links

Cognitive Dimensions of Notation Resource Site

Cognitive dimensions
at usabilityfirst.com glossary
Cognitive Dimensions of Information Artefacts: a tutorial
by Thomas Green and Alan Blackwell
A Usable Guide to Cognitive Dimensions
and intuitive explanation of Cognitive Dimensions Usability Human–computer interaction Programming language topics Notation User interface techniques Usability inspection