Declarative Datalog Debugging for Mere Mortals

Tracing why a "faulty" fact A is in the model M=P(I) of program P on input I quickly gets tedious, even for small examples. We propose a simple method for debugging and "logically profiling" P by generating a provenance-enriched rewriting P, which records rule firings according to the logical semantics. The resulting provenance graph can be easily queried and analyzed using a set of predefined and ad-hoc queries. We have prototypically implemented our approach for two different Datalog engines (DLV and LogicBlox), demonstrating the simplicity, effectiveness, and system-independent nature of our method.