Software metrics: successes, failures and new directions

The history of software metrics is almost as old as the history of software engineering. Yet, the extensive research and literature on the subject has had little impact on industrial practice. This is worrying given that the major rationale for using metrics is to improve the software engineering decision making process from a managerial and technical perspective. Industrial metrics activity is invariably based around metrics that have been around for nearly 30 years (notably Lines of Code or similar size counts, and defects counts). While such metrics can be considered as massively successful given their popularity, their limitations are well known, and mis-applications are still common. The major problem is in using such metrics in isolation. We argue that it is possible to provide genuinely improved management decision support systems based on such simplistic metrics, but only by adopting a less isolationist approach. Specifically, we feel it is important to explicitly model: (a) cause and effect relationships and (b) uncertainty and combination of evidence. Our approach uses Bayesian Belief nets, which are increasingly seen as the best means of handling decisionmaking under uncertainty. The approach is already having an impact in Europe. (C) 1999 Elsevier Science Inc. All rights reserved.