Most studies of software failures and faults have done little more than classify failures and faults collected from long-term projects. The authors propose a model to analyze failures and faults for debugging purposes. In the model, they define "failure modes" and "failure types" to identify the existence of program failures and the nature of the program failures, respectively. The goal of this research is to achieve a systematic process model to localize faults in debugging. They first examine properties of the proposed model from a theoretical point of view, then use the trityp program as a simple example to illustrate the possible usage of the model for debugging. Further study of the failure mode, a pilot experiment of applying the proposed model, and a way to employ heuristics according to different situations for fault localization are areas of future work.

Developing effective debugging strategies to guarantee the reliability of software is important. By analyzing the debugging process used by experienced programmers, we have found that four distinct tasks are consistently performed: (1) determining statements involved in program failures, (2) selecting suspicious statements that might contain faults, (3) making hypotheses about suspicious faults (variables and locations), and (4) restoring program state to a specific statement for verification. This research focuses support for the second task, reducing the search domain for faults, which we refer to as fault localization.We explored a new approach to enhancing the process of fault localization based on dynamic program slicing and mutation-based testing. In this new approach, we have developed the technique of Critical Slicing to enable debuggers to highlight suspicious statements and thus to confine the search domain to a small region. The Critical Slicing technique is partly based on "statement deletion" mutant operator of the mutation-based testing methodology. We have explored properties of Critical Slicing, such as the relationship among Critical Slicing, Dynamic Program Slicing, and Executable Static Program Slicing; the cost to construct critical slices; and the effectiveness of Critical Slicing. Results of experiments support our conjecture as to the effectiveness and feasibility of using Critical Slicing for fault localization.This paper explains our technique and summarizes some of our findings. From these, we conclude that a debugger equipped with our proposed fault localization method can reduce human interaction time significantly and aid in the debugging of complex software.