Glossary » Design Principles

2-second rule

A loose principle that a user should not need to wait more than 2 seconds for certain types of system response, such as application-switching and application launch time. The choice of 2 seconds is somewhat arbitrary, but a reasonable order…

3-click rule

The principle that access to any feature of an application, or each logical step in a process, should require no more than 3 clicks. Applying this principle can be tricky because of the ill-defined nature of what constitutes a primary…

80/20 rule

A principle for setting priorities: users will use 20% of the features of your product 80% of the time. Focus the majority of your design and development effort (80%) on the most important 20% of the product.

accountability

the principle that in many multi-user situations, someone must be identifiable in order to take responsibility for actions or for decisions. In these cases, anonymity is not always effective or achievable (though users may be anonymous to other users while…

aesthetic integrity

a principle that advocates that a design should be visually appealing and should follow common principles of visual design: consistency, a clear identity, a clear visual hierarchy, good alignment, contrast, and proportions, etc.

What constitutes an aesthetically successful design may…

affordance

a situation where an object’s sensory characteristics intuitively imply its functionality and use.

A button, by being slightly raised above an otherwise flat surface, suggests the idea of pushing it. A lever, by being an appropriate size for grasping, suggests…

AIDA

Attention, Interest, Desire, Action. This classic advertising model says that an advertisement (and by extension, many effective user interfaces) ought to function by getting people’s attention, stimulating their interest, generating a desire, and then finishing with a call to action.…

anonymity

the ability to participate in interactions with other people without being identified. Anonymity can be at various levels, including hiding a person’s name and other characteristics, such as age and gender; from simply making their name accessible but nonobvious, to…

anticipation

in animation, preparation before an action so that the user has some foreshadowing of the action and can more effectively interpret the action. For instance, when a character runs away, the character will back off slightly in the opposite direction…

articulatory directness

how well the form and behavior of an input device (degrees of freedom, range of motion, discreteness of states) corresponds to the type of input values a user needs to express.

attention to detail

a design philosophy that emphasizes that what may appear to be insignificant details can determine whether a design succeeds. A design should be fully unified at every level of granularity.

attitude measure

a quantitative value representing the subjective rating or opinion of users reacting to seeing or using a system, as opposed to performance measures like task completion time or number of errors.

automaticity

a level of skilled performance characterized by high speed, minimal errors, inability to verbally describe the thought process, and low interference with other simultaneous activities.

automation

using a computer to perform a task previously done by a human; the principle that if the user would always do the same well-defined task in a given context, then the computer ought to just go ahead and do it.…

awareness

the sense of what other people are doing, even when you’re not communicating with them directly.

Awareness is useful for coordinating with others in collaborative tasks where direct communication is not always necessary. Awareness also refers to indirect forms of…

bandwidth

the amount of data that can be transmitted across a network during a given period of time. Variance in bandwidth is also an important measure.

baseline

baseline is basically where things “are” in the sense that what we see is what is being done by a “majority” within a competitive space. Now you could argue that, because most are doing something, more audiences experience the same…

benchmarks

ways of measuring the degree of usability of a system. Examples of these include time to perform a task, number of errors, time to learn a system, and how a user feels after using a system.

best practices

the things that we do in recognition and presentation of natural workflows, hierarchies and priorities, cues, integration (physical vs. mental), etc. Labels, on the other hand, come and go — best practices endure, for the most part, longer than labels…

call control

same as session control; the mechanism for determining who is involved in a call (session) and for setting up the call. A call is the term used most frequently for telephone sessions. The term session is used more often in…

capture error

a type of slip (a kind of error) where a more frequent and more practiced behavior takes place when a similar, but less familiar, action was intended. Examples include telling someone your home phone number when you intended to give…

chromostereopsis

a phenomenon of visual perception: different wavelengths of light focus at slightly different depths in the eye. Thus, it is difficult to focus on an image that combines two colors because each color is fuzzy when the other color is…

clearly marked exits

a principle that users should be able to easily cancel or undo an undesirable operation; essentially the principle of reversibility or forgiveness. Examples include:

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cognitive dimensions

T.R.G. Green’s design principles for notations & programming language design. He emphasizes that because there are tradeoffs among these, they cannot be “guidelines” but must be viewed as discussion points, but of course, all guidelines involve tradeoffs.

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cognitive load

the level of effort associated with thinking and reasoning (including perception, memory, language, etc.), thus potentially interfering with other thought processes. A user interface strives to minimize the cognitive load associated with operating the interface itself so that all of…