Combined approach 1 Conjunctive queries 1 Conjunctive query 1 Data description 1 Existential rule 1 Existential rules 1 Guardedness Modeling languages 1 Ontological query 1 Ontologies 1 Ontology 1 Ontology's 1 Polynomial approximation 1 Query answering 1 Query languages 1 Query processing 1 Query rewriting 1 Query rewritings 1 Rewritten query 1 Search engines 1 Tuple-generating dependencies 1