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rates or cost. Some studies have shown that both McCabe and Halstead do no better
at predicting error rates and cost than simple lines-of-code measurements. Studies
that attempt to correlate error rates with computed complexity measures show mixed
results. Some studies have shown that experienced programmers provide the best
prediction of error rates and software complexity.
5.4
GQM (GOAL-QUESTION-METRIC) APPROACH
Goal-oriented measurement points out that the existence of the explicitly stated goal
is of the highest importance for improvement programs. GQM presents a systematic
approach for integrating goals to models of the software processes, products, and
quality perspectives of interest based on the specific needs of the project and the
organization (Basili et al., 1994).
In other words, this means that in order to improve the process, the team has to
define measurement goals, which will be, after applying the GQM method, refined
into questions and consecutively into metrics that will supply all the necessary infor-
mation for answering those questions. The GQM method provides a measurement
plan that deals with the particular set of problems and the set of rules for obtained
data interpretation. The interpretation gives us the answer if the project goals were
attained.
GQM defines a measurement model on three levels: Conceptual level (goal),
operational level (question), and quantitative level (metric). A goal is defined for
an object for a variety of reasons, with respect to various models of quality, from
various points of view, and relative to a particular environment. A set of questions is
used to define the models of the object of study and then focuses on that object to
characterize the assessment or achievement of a specific goal. A set of metrics, based
on the models, is associated with every question in order to answer it in a measurable
way. Questions are derived from goals that must be answered in order to determine
whether the goals are achieved. Knowledge of the experts gained during the years of
experience should be used for GQM definitions. These developers' implicit models
of software process and products enable the metric definition.
Two sets of metrics now can be mutually checked for consistency and complete-
ness. The GQM plan and the measurement plan can be developed, consecutively;
data collection can be performed; and finally, the measurement results are returned
to the project members for analysis, interpretation, and evaluation on the basis of the
GQM plan.
The main idea is that measurement activities always should be preceded by iden-
tifying clear goals for them. To determine whether the team has met a particular
goal, the team asks questions whose answers will tell them whether the goals have
been achieved. Then, the team generates from each question the attributes they must
measure to answer these questions.
Sometimes a goal-oriented measurement makes common sense, but there are
many situations where measurement activities can be crucial even though the goals
are not defined clearly. This is especially true when a small number of metrics address
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