Ontologies for Knowledge Graphs: Breaking the Rules [chapter]

Markus Krötzsch, Veronika Thost
2016 Lecture Notes in Computer Science  
Large-scale knowledge graphs (KGs) are widely used in industry and academia, and provide excellent use-cases for ontologies. We find, however, that popular ontology languages, such as OWL and Datalog, cannot express even the most basic relationships on the normalised data format of KGs. Existential rules are more powerful, but may make reasoning undecidable. Normalising them to suit KGs often also destroys syntactic restrictions that ensure decidability and low complexity. We study this issue
more » ... r several classes of existential rules and derive new syntactic criteria to recognise well-behaved rule-based ontologies over KGs. Frontier Guardedness and Functional Attributes Our denormalisation procedure can also be applied to KG frontier guarded rules. Theorem 8. If P is KG frontier guarded and Algorithm 1 terminates on P, then the denormalised rule set Result P is frontier guarded. This follows since a KG frontier guarded rule can only have one object variable in its frontier, so that the object in this case must be the guard. Rewriting therefore can only increase the size of the guard, preserving frontier guardedness.
doi:10.1007/978-3-319-46523-4_23 fatcat:i3jgivfb75hdbdohmocj34svfa