Usability is a term used to denote the ease with which people can employ a particular tool or other human-made object in order to achieve a particular goal. Usability can also refer to the methods of measuring usability and the study of the principles behind an object's perceived efficiency or elegance.

In human-computer interaction, usability usually refers to the elegance and clarity with which the user interface of a computer program or web site is designed. The primary notion of usability is that an object designed with the users' psychology and physiology in mind are, for example:

  • More efficient to use—it takes less time to accomplish a particular task
  • Easier to learn—operation can be learned by observing the object
  • More satisfying to use

Complex computer systems are finding their way into everyday life, and at the same time the market is becoming saturated with competing brands. This has led to usability becoming more popular and widely recognised in recent years as companies see the benefits of researching and developing their products with user-oriented instead of technology-oriented methods. By understanding and researching the interaction between product and user, the usability expert can also provide insight that is unattainable by traditional company-oriented market research. For example, after observing and interviewing users, the usability expert may identify needed functionality or design flaws that were not anticipated.

In the user-centered design paradigm, the product is designed with its intended users in mind at all times. In the user-driven or participatory design paradigm, some of the users become actual members of the design team.

ISO standard Edit

The document ISO 9126 (1991) Software Engineering Product Quality issued by International Organization for Standardization defines usability as:

A set of attributes that bear on the effort needed for use, and on the individual assessment of such use, by a stated or implied set of users.

The document ISO 9241-11 (1998) Guidance on Usability also issued by International Organization for Standardization defines usability as:

The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.

Jakob Nielsen's framework of system acceptability Edit

Usability consultant Jakob Nielsen and computer science professor Ben Shneiderman have written (separately) about a framework of system acceptability, where usability is a part of usefulness and is composed of:

  • Learnability (e.g. intuitive navigation)
  • Efficiency of use
  • Memorability
  • Few and noncatastrophic errors
  • Subjective satisfaction

Usability considerations Edit

Usability includes considerations such as:

  • Who are the users, what do they know, and what can they learn?
  • What do users want or need to do?
  • What is the general background of the users?
  • What is the context in which the user is working?
  • What has to be left to the machine? What to the user?

Answers to these can be obtained by conducting user and task analysis at the start of the project.

Other considerations include:

  • Can users easily accomplish their intended tasks? For example, can users accomplish intended tasks at their intended speed?
  • How much training do users need?
  • What documentation or other supporting materials are available to help the user? Can users find the solutions they seek in these materials?
  • What and how many errors do users make when interacting with the product?
  • Can the user recover from errors? What do users have to do to recover from errors? Does the product help users recover from errors, for example, does software present comprehensible, informative, non-threatening error messages?
  • Are there provisions for meeting the special needs of users with disabilities? (accessibility)

Examples of ways to find answers to these and other questions are: user-focused requirements analysis, building user profiles, and usability testing.

Usability is now recognized as an important software quality attribute, earning its place among more traditional attributes such as performance and robustness. Indeed various academic programs focus on usability. [1] Also several usability consultancy companies have emerged, and traditional consultancy and design firms are offering similar services.

External Links Edit

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