Software Engineering for Students A Programming Approach

364 Chapter 29 ■ Software metrics and quality assurance
be used to measure maintainability. Reliability can be measured as MTTF. However, for
many of these attributes, it is extremely difficult to make an accurate judgment and a
subjective guess must suffice – with all its uncertainties.
SELF-TEST QUESTION
29.3 List some other quality factors that can be quantified.
29.6 ● Quality assurance
Quality assurance means ensuring that a software system meets its quality goals. The
goals differ from one project to another. They must be clear and can be selected from
the list of quality factors we saw earlier. To achieve its goals, a project must use effective
tools and methods. Also checks must be carried out during the development process at
every available opportunity to see that the process is being carried out correctly.
To ensure that effective tools and methods are being used, an organization distills its
best practices and documents them in a quality manual. This is like a library of all the
effective tools, methods and notations. It is like a recipe book in cooking, except that
it contains only the very best recipes. This manual describes all the standards and procedures
that are available to be used.
A standard defines a range, limit, tolerance or norm of some measurable attribute
against which compliance can be judged. For example, during white box testing, every
source code statement must be executed at least once. In the kitchen, all peeled potatoes
must be inspected to ensure there is no skin remaining on them.
A procedure prescribes a way of doing something (rules, steps, guidelines, plans). For
example, black box testing, white box testing and a walkthrough must be used to verify
each component of software. In the kitchen, all green vegetables will be steamed,
rather than boiled.
To be effective, quality assurance must be planned in advance – along with the planning
of all other aspects of a software project. The project manager:
1. decides which quality factors are important for the particular project (e.g. high reliability
and maintainability). In preparing a family meal, perhaps flavor and nutritional
value are the paramount goals.
2. selects standards and procedures from the quality manual that are appropriate to
meeting the quality goals (e.g. the use of complexity metrics to check maintainability).
If the meal does not involve potatoes, then those parts of the quality manual
that deal with potatoes can be omitted.
3. assembles these into a quality assurance plan for the project. This describes what
the procedures and standards are, when they will be done, and who does them.
More and more the organizations that produce software are having to convince their
customers that they are using effective methods. More and more commonly they must