Polynomial Combined Rewritings for Existential Rules

Polynomial Combined Rewritings for Linear Existential Rules and DL-Lite with n-ary Relations

Polynomial Rewritings for Linear Existential Rules

We consider the scenario of ontology-based query answering. It is generally accepted that true scalability in this setting can only be achieved via query rewriting, which in turn allows for the exploitation of standard RDBMSs. In this work, we close two open fundamental questions related to query rewriting. We establish that linear existential rules are polynomially combined rewritable, while f...

Query Rewriting over Shallow Ontologies

We investigate the size of conjunctive query rewritings over OWL2QL ontologies of depth 1 and 2 by means of a new formalism, called hypergraph programs, for computing Boolean functions. Both positive and negative results are obtained. All conjunctive queries over ontologies of depth 1 have polynomial-size nonrecursive datalog rewritings; tree-shaped queries have polynomial-size positive existen...

Ontology-Mediated Queries: Combined Complexity and Succinctness of Rewritings via Circuit Complexity

We give solutions to two fundamental computational problems in ontologybased data access with the W3C standard ontology language OWL2QL: the succinctness problem for first-order rewritings of ontology-mediated queries (OMQs), and the complexity problem for OMQ answering. We classify OMQs according to the shape of their conjunctive queries (treewidth, the number of leaves) and the existential de...

The price of query rewriting in ontology-based data access

We give a solution to the succinctness problem for the size of first-order rewritings of conjunctive queries in ontologybased data access with ontology languages such as OWL 2 QL , linear Datalog± and sticky Datalog±. We show that positive existential and nonrecursive datalog rewritings, which do not use extra non-logical symbols (except for intensional predicates in the case of datalog rewriti...