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80 PART TWO MANAGING SOFTWARE PROJECTS

QUICK What is the work product? A set How do I ensure that I’ve done it right? By apply-
LOOK of software metrics that provide ing a consistent, yet simple measurement scheme
insight into the process and that is never to be used to assess, reward, or pun-
understanding of the project. ish individual performance.

Within the context of software project management, we are concerned primarily
XRef with productivity and quality metrics—measures of software development "output"
Technical metrics for as a function of effort and time applied and measures of the "fitness for use" of the
software engineering
are presented in work products that are produced. For planning and estimating purposes, our inter-
Chapters 19 and 24. est is historical. What was software development productivity on past projects? What
was the quality of the software that was produced? How can past productivity and
quality data be extrapolated to the present? How can it help us plan and estimate
more accurately?
In their guidebook on software measurement, Park, Goethert, and Florac [PAR96]
discuss the reasons that we measure:
There are four reasons for measuring software processes, products, and resources: to char-
acterize, to evaluate, to predict, or to improve.
We characterize to gain understanding of processes, products, resources, and environ-
ments, and to establish baselines for comparisons with future assessments.
We evaluate to determine status with respect to plans. Measures are the sensors that
let us know when our projects and processes are drifting off track, so that we can bring
them back under control. We also evaluate to assess achievement of quality goals and to
assess the impacts of technology and process improvements on products and processes.
“Software metrics let We predict so that we can plan. Measuring for prediction involves gaining understand-
you know when to ings of relationships among processes and products and building models of these rela-
laugh and when to tionships, so that the values we observe for some attributes can be used to predict others.
cry.”
We do this because we want to establish achievable goals for cost, schedule, and quality—
Tom Gilb
so that appropriate resources can be applied. Predictive measures are also the basis for
extrapolating trends, so estimates for cost, time, and quality can be updated based on cur-
rent evidence. Projections and estimates based on historical data also help us analyze risks
and make design/cost trade-offs.
We measure to improve when we gather quantitative information to help us identify
roadblocks, root causes, inefficiencies, and other opportunities for improving product qual-
ity and process performance.

4.1 MEASURES, METRICS, AND INDICATORS
Although the terms measure, measurement, and metrics are often used interchange-
ably, it is important to note the subtle differences between them. Because measure