Attempts to reduce the number of delivered faults in software are estimated to consume 50% to 80% of the development and maintenance effort according to J.S. Collofello ans S.N. Woodfield (1989). Among the tasks required to reduce the number of delivered faults, debugging is one of the most time-consuming according to T. Ball and S.G. Eick and Telcordia Technologies, and locating the errors is the most difficult component of this debugging task according to I. Vessey (1985). Clearly, techniques that can reduce the time required to locate faults can have a significant impact on the cost and quality of software development and maintenance.