This article presents an improved approach to assist diagnosis of failures in software (fault localisation) by ranking program statements or blocks in accordance with to how likely they are to be buggy. We present a very simple single-bug program to model the problem. By examining different possible execution paths through this model program over a number of test cases, the effectiveness of different proposed spectral ranking methods can be evaluated in idealised conditions. The results are remarkably consistent to those arrived at empirically using the Siemens test suite and Space benchmarks. The model also helps identify groups of metrics that are equivalent for ranking. Due to the simplicity of the model, an optimal ranking method can be devised. This new method out-performs previously proposed methods for the model program, the Siemens test suite and Space. It also helps provide insight into other ranking methods.

No abstract

No abstract

No abstract

Numerous set similarity metrics have been used for ranking "suspiciousness" of code in spectral fault localization, which uses execution profiles of passed and failed test cases to help locate bugs. Research in data mining has identified several forms of possibly desirable symmetry in similarity metrics. Here we define several forms of "duals" of metrics, based on these forms of symmetries. Use of these duals, plus some other slight modifications, leads to several new similarity metrics. We show that versions of several previously proposed metrics are optimal, or nearly optimal, for locating single bugs. We also show that a form of duality exists between locating single bugs and locating "deterministic" bugs (execution of which always results in test case failure). Duals of the various single bug optimal metrics are optimal for locating such bugs. This more theoretical work leads to a conjecture about how different metrics could be chosen for different stages of software development.

This paper describes a simpler way for programmers to reason about the correctness of their code. The study of semantics of logic programs has shown strong links between the model theoretic semantics (truth and falsity of atoms in the programmer's interpretation of a program), procedural semantics (for example, SLD resolution) and fixpoint semantics (which is useful for program analysis and alternative execution mechanisms). Most of this work assumes that intended interpretations are two-valued: a ground atom is true (and should succeed according to the procedural semantics) or false (and should not succeed). In reality, intended interpretations are less precise. Programmers consider that some atoms "should not occur" or are "ill-typed" or "inadmissible". Programmers don't know and don't care whether such atoms succeed. In this paper we propose a three-valued semantics for (essentially) pure Prolog programs with (ground) negation as failure which reflects this. The semantics of Fitting is similar but only associates the third truth value with nontermination. We provide tools to reason about correctness of programs without the need for unnatural precision or undue restrictions on programming style. As well as theoretical results, we provide a programmer-oriented synopsis. This work has come out of work on declarative debugging, where it has been recognised that inadmissible calls are important. This paper has been accepted to appear in Theory and Practice of Logic Programming.

No abstract

No abstract