Software quality attributes (Bass, Clements, and Kazman 2003) refer to the nonfunctional requirements of software, which can have a profound effect on the quality of a software product. Many of these attributes can be addressed and evaluated at the time the software architecture is developed. Software quality attributes include maintainability, modifiability, testability, traceability, scalability, reusability, performance, availability, and security. An introduction to software quality attributes is given in Section 4.6. This section describes each of these attributes and discusses how they are supported by the COMET design method.

Some software quality attributes are also system quality attributes because they need both the hardware and software to achieve high quality. Examples of these quality attributes are performance, availability, and security. Other software quality attributes are purely software in nature because they rely entirely on the quality of the software. Examples of these quality attributes are maintainability, modifiability, testability, and traceability.

MAINTAINABILITY

Maintainability is the extent to which software is capable of being changed after deployment. Software may need to be modified for the following reasons:

• Fix remaining errors. These are errors that were not detected during testing of the software prior to deployment.

• Address performance issues. Performance problems may not become apparent until after the software application has been deployed and is operational in the field.

• Changes in software requirements. The biggest reason for software change is changes in software requirements.