Locating causes of program failures

Which is the defect that causes a software failure? By comparing the program states of a failing and a passing run, we can identify the state differences that cause the failure. However, these state differences can occur all over the program run. Therefore, we focus in space on those variables and values that are relevant for the failure, and in time on those moments where cause transitions occur - moments where new relevant variables begin being failure causes: "Initially, variable argc was 3; therefore, at shell-sort(), variable a2 was 0, and therefore, the program failed." In our evaluation, cause transitions locate the failure-inducing defect twice as well as the best methods known so far.