Usability and Quality
Quality is an attribute of a product or service is misleading, as the
attributes required for quality will depend on how the product is used.
Quality of use is therefore defined as the extent to which a product or
service satisfies stated and implied needs when used under stated conditions.
Quality of use can be used to measure usability as the extent to which
specified goals can be achieved with effectiveness, efficiency and satisfaction
by specified users carrying out specified tasks in specified environments.
1. What is usability?
Web usability as an objective is synonymous with quality of use, ie
that the web site can be used in the real world. Thus usability has two
complementary roles in design: as an attribute which must be designed
into a web site, and as the highest level quality objective which should
be the overall objective of design.
What is quality?
There is a close analogy between different interpretations of the term
usability and comparable interpretations of the term quality. Although
the term quality seems self-explanatory in everyday usage, in practice
there are many different views of what it means and how it should be achieved
as part of a web production process.
A simple analysable property which is recognised through experience
Usablequality: an inherent characteristic of the web site determined
by the presence or absence of measurable functional and content attributes.
Production quality: a web site which conforms to specified requirements.
User perceived quality: the combination of web site attributes
which provide the greatest satisfaction to a specified user.
If different groups of users have different needs, then they may require
different characteristics for a web site to have quality, so that assessment
of quality becomes dependent on the perception of the user.
ISO 9126 takes this approach and categorises the attributes of software
quality as: functionality, efficiency, usability, reliability, maintainability
Quality and usability Comparison
Some compare usability to quality assurance. There are important similarities:
Both seek to improve system quality; both are cost-effective; both can
reduce development time. However, they are not identical.
Usability focuses on the user interface, on the elements the end user
directly interacts with, and the quality-of-use issues users directly
encounters: screen layout, colors, menus, error messages; consistency,
navigation, orientation, etc. Usability engineering's purpose is to enhance
the quality of the end-user's experience while quality assurance focuses
on elements that users do not interact with directly, such as code integrity.
Quality assurance is now familiar to most software professionals, but
most software professionals are not as familiar with usability engineering.
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