Critical slice and its application to program debugging

Existing algorithmic debugging methods which can locate faults under the guidance of a system have a number of problems. For example, they cannot be applied to imperative languages with side effects, or they can locate a faulty function but not a faulty statement, or they cannot detect faults related to missing statements. This paper presents an algorithmic critical slice-based fault-locating method for imperative languages. The paper first classifies program faults into two categories : wrong-value faults and missing-assignment faults. The critical slice with respect to a variable-value error is a set of statements such that (1) a wrong-value fault contained in any instruction in the critical slice may have caused that variable-value error, and (2) a wrong-value fault contained in any instruction outside the critical slice could definitely not have caused that variable-value error. The paper then shows that it is possible to algorithmically locate any fault, including missing statements, by dividing the critical slice at a certain point and then examining the values of the flow-data, which are the variables whose values are flowing across that division point.