2.8 Software quality management

Introduction

What is software quality, and why is it so important that it is pervasive in the Software Engineering Body of Knowledge? Within an information system, software is a tool, and tools have to be selected for quality and for appropriateness. That is the role of equirements. But software is more than a tool. It dictates the performance of the system, and it is therefore important to the system quality.

The notion of “quality” is not as simple as it may seem. For any engineered product, there are many desired qualities relevant to a particular project, to be discussed and determined at the time that the product requirements are determined. Qualities may be present or absent, or may be matters of degree, with tradeoffs among them, with practicality and cost as major considerations. The software engineer has a responsibility to elicit the system’s quality requirements that may not be explicit at the outset and to discuss their importance and the difficulty of attaining them. All processes associated with software quality (e.g. building, checking, improving quality) will be designed with these in mind

and carry costs based on the design. Thus, it is important to have in mind some of the possible attributes of quality.

Various researchers have produced models (usually taxonomic) of software quality characteristics or attributes that can be useful for discussing, planning, and rating the quality of software products. The models often include metrics to “measure” the degree of each quality attribute the product attains.

Usually these metrics may be applied at any of the product levels. They are not always direct measures of the quality characteristics of the finished product, but may be relevant to the achievement of overall quality. Each model may have a different set of attributes at the highest level of the taxonomy, and selection of and definitions for the attributes at all levels may differ. The important point is that the system software requirements define the quality requirements and the definitions of the attributes for them.

Software quality fundamentals

Agreement on quality requirements, as well as clear communication to the software engineer on what constitutes quality, require that the many aspects of quality be formally defined and discussed.

A software engineer should understand the underlying meanings of quality concepts and characteristics and their value to the software under development or to maintenance.

The important concept is that the software requirements define the required quality characteristics of the software and influence the measurement methods and acceptance criteria for assessing these characteristics.