Safety as a metric

Most software metrics measure the syntactic qualities of a program. While measuring such properties may reveal problems in programs, these metrics fail to measure the essence of programs: (partial) correctness and robustness. We therefore propose to base metrics on semantic, instead of syntactic, criteria. To illustrate the idea of semantics-based metrics, we have built static debuggers, which are tools that detect potential run-time failures. More specifically, a static debugger analyses programs written in safe programming languages and pinpoints those program operations that might trigger a run-time error. This paper briefly recalls what safety means for a programming language. It then sketches how a static debugger works and the role it plays in measuring the robustness of a program. The last section discusses the use of static debuggers in the classroom, an NSF Educational Innovation Project.