Sommerville-Software-Engineering-10ed

24.5 ■ Software measurement 719
1. The internal attribute must be measured accurately. However, measurement is
not always straightforward and may require specially developed tools.
2. A relationship must exist between the attribute that can be measured and the external
quality attribute that is of interest. That is, the value of the quality attribute
must be related, in some way, to the value of the attribute than can be measured.
3. This relationship between the internal and external attributes must be understood,
validated, and expressed in terms of a formula or model. Model formulation
involves identifying the functional form of the model (linear, exponential, etc.)
by analysis of collected data, identifying the parameters that are to be included
in the model and calibrating these parameters using existing data.
Recent work in the area of software analytics (Zhang et al. 2013) has used datamining
and machine-learning techniques to analyze repositories of software product
and process data. The idea behind software analytics (Menzies and Zimmermann
2013) is that we do not, in fact, need a model that reflects the relationships between
software quality and collected data. Rather, if there is enough data, correlations can
be discovered and predictions made about software attributes. I discuss software
analytics in Section 24.5.4.
We have very little published information about systematic software measurement
in industry. Many companies do collect information about their software,
such as the number of requirements change requests or the number of defects
discovered in testing. However, it is not clear if they then use these measurements
systematically to compare software products and processes or assess the impact
of changes to software processes and tools. There are several reasons why this
is difficult:
1. It is impossible to quantify the return on investment of introducing an organizational
metrics or software analytics program. We have seen significant improvements
in software quality over the past few years without the use of metrics, so
it is difficult to justify the initial costs of introducing systematic software measurement
and assessment.
2. There are no standards for software metrics or standardized processes for measurement
and analysis. Many companies are reluctant to introduce measurement
programs until such standards and supporting tools are available.
3. Measurement may require the development and maintenance of specialized
software tools. It is difficult to justify the costs of tool development when the
returns from measurement are unknown.
4. In many companies, software processes are not standardized and are poorly
defined and controlled. As such, there is too much process variability within the
same company for measurements to be used in a meaningful way.
5. Much of the research on software measurement and metrics has focused on
code-based metrics and plan-driven development processes. However, more and
more software is now developed by reusing and configuring existing application