Matching with respect to general concept inclusions in the Description Logic EL

ABSTRACT. Matching concept descriptions against concept patterns was introduced as a new inference task in Description Logics almost 20 years ago, motivated by applications in the Classic system. For the Description Logic EL, it was shown in 2000 that the matching problem is NP-complete. It then took almost 10 years before this NP-completeness result could be extended from matching to unification in EL. The next big challenge was then to further extend these results from matching and unification without a TBox to matching and unification w.r.t. a general TBox, i.e., a finite set of general concept inclusions. For unification, we could show some partial results for general TBox that satisfy a certain restriction on cyclic dependencies between concepts, but the general case ist still open. For matching, we solve the general case in this paper: we show that matching in EL w.r.t. general TBoxes is NP-complete by introducing a goal-oriented matching algorithm that uses nondeterministic rules to transform a given matching problem into a solved form by a polynomial number of rule applications. We also investigate some tractable variants of the matching problem.