Information Technology Reference
In-Depth Information
12.2.3 ISO 9126 Quality Factors
When measuring product quality it is helpful to have general guidelines to follow
as you assess a system. The ISO 9126 quality factors define six attributes (each
containing sub-attributes) in its model of quality for organizations to use as a
general checklist. These qualities include):
• Functionality defines how well needs are satisfied by software under the sub-
attributes of suitability, accuracy, interoperability, security, and compliance.
• Reliability describes the period of time for which the software will perform its
purpose indicated by maturity, fault tolerance, and recoverability.
• Usability indicates the ease-of-use of the software as defined by its undert-
sandability, learnability, and operability.
• Efficiency is the extent to which software makes effective use of system
resources; included in efficiency is time behavior, and resource behavior.
• Maintainability describes how easily a repair or revision is able to be made to
software. This can be described by the sub-attributes of analyzability, change-
ability, testability, and stability.
• Portability is defined by a system's adaptability, conformance, installability,
and replaceability.
These guidelines are, of course, very general and leave much room for speci-
fication to the individual organizations.
12.2.4 The Quantitative View
The McCall's, Garvin's, and ISO 9126 quality factors, among others, define a very
general way to describe the quality of software, however, more exact measures
should be preferred when assessing software. The primary problem with using the
previously defined quality factors is the level of subjectivity required when directly
applying them. Therefore, we will define quantitative measures in subsequent
sections that allow us to indirectly measure software quality; this can be done by
measuring those attributes of software that allow for such exact metrics which also
represent some manifestation of software quality. By doing so we eliminate much
of the subjective nature of software quality assessment.
12.3 Design Metrics
The need for design metrics stems from the need for quality design. The design of
a program directly impacts the maintainability, efficiency, and adaptability of the
software, and a well-written piece of software aims to be easily modified, easy to
