Logic-based Semantics and Query Entailment for RDFS Knowledge Graphs (Extended Abstract)

This extended abstract summarises our recent investigation on RDFS-based Knowledge Graphs (RKGs). Inspired by previous work on equipping DLs with a semantics adequate for metamodeling, we provide a formal semantics for RKGs based on classical logic. We show that, surprisingly, under the newly defined semantics, RKGs do not admit, in general, a universal model. Also, we introduce the notions of definite and indefinite RKGs and show that being definite is both a sufficient and necessary condition for an RKG to admit a universal model, thus singling out the source of incompleteness that causes the lack of a universal model for indefinite RKGs. Finally, we characterize the complexity of the query answering problem for both definite and indefinite RKGs.