Introduction to Software metrics

Software metrics are an integral part of the state of the practice in software engineering. More and more customers are specifying software and/or quality
metrics reporting as part of their contractual requirements.Software metrics provide a quantitative way to assess the quality of internal product attributes, thereby enabling a software engineer to assess quality before the product is built.
Good metrics should facilitate the development of models that are capable of predicting process or product parameters, not just describing them. Thus, ideal metrics should be :
- simple, precisely definable — so that it is clear how the metric can be evaluated.
- objective, to the greatest extent possible.
- easily obtainable.
- valid — the metric should measure what it is intended to measure.
- robust—relatively insensitive to (intuitively) insignificant changes in the process or product.

Software metrics may be broadly classified as :
- Product and Process Metrics : Product metrics are measures of the software product at any stage of its development, from requirements to installed system. Product metrics may measure the complexity of the software design, the size of the final program or the number of pages of documentation produced. Process metrics, on the other hand, are measures of the software development process, such as overall development time, type of methodology used, or the average level of experience of the programming staff.
- Objective and Subjective Metrics : Objective metrics should always result in identical values for a given metric, as measured by two or more qualified observers.
For subjective metrics, even qualified observers may measure different values for a given metric, since their subjective judgment is involved in arriving at the measured value.
- Primitive and Computed Metrics : Primitive metrics are those that can be directly observed, such as the program size (in LOC), number of defects observed in unit testing, or total development time for the project. Computed metrics are those that cannot be directly observed but are computed in some manner from other metrics.