Decidable optimization problems for database logic programs
STOC '88 Proceedings of the twentieth annual ACM symposium on Theory of computing
Reasoning about The Past with Two-Way Automata
ICALP '98 Proceedings of the 25th International Colloquium on Automata, Languages and Programming
Tractable Reasoning and Efficient Query Answering in Description Logics: The DL-Lite Family
Journal of Automated Reasoning
Reasoning in Description Logics by a Reduction to Disjunctive Datalog
Journal of Automated Reasoning
Homomorphism preservation theorems
Journal of the ACM (JACM)
Query Answering in the Description Logic Horn-$\mathcal{SHIQ}$
JELIA '08 Proceedings of the 11th European conference on Logics in Artificial Intelligence
Boundedness of Monadic Second-Order Formulae over Finite Words
ICALP '09 Proceedings of the 36th Internatilonal Collogquium on Automata, Languages and Programming: Part II
IJCAI'05 Proceedings of the 19th international joint conference on Artificial intelligence
Deciding inseparability and conservative extensions in the description logic EL
Journal of Symbolic Computation
Consequence-driven reasoning for horn SHIQ ontologies
IJCAI'09 Proceedings of the 21st international jont conference on Artifical intelligence
Conjunctive query answering in the description logic EL using a relational database system
IJCAI'09 Proceedings of the 21st international jont conference on Artifical intelligence
Efficient Query Answering for OWL 2
ISWC '09 Proceedings of the 8th International Semantic Web Conference
Eliminating recursion in the µ-calculus
STACS'99 Proceedings of the 16th annual conference on Theoretical aspects of computer science
Ontological queries: Rewriting and optimization
ICDE '11 Proceedings of the 2011 IEEE 27th International Conference on Data Engineering
Optimized query rewriting for OWL 2 QL
CADE'11 Proceedings of the 23rd international conference on Automated deduction
Parity games played on transition graphs of one-counter processes
FOSSACS'06 Proceedings of the 9th European joint conference on Foundations of Software Science and Computation Structures
Ontology-based data access: a study through disjunctive datalog, CSP, and MMSNP
Proceedings of the 32nd symposium on Principles of database systems
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One of the most advanced approaches to querying data in the presence of ontologies is to make use of relational database systems, rewriting the original query and the ontology into a new query that is formulated in SQL or, equivalently, in first-order logic (FO). For ontologies written in many standard description logics (DLs), however, such FO-rewritings are not guaranteed to exist. We study FO-rewritings and their existence for a basic class of queries and for ontologies formulated in Horn DLs such as Horn-SHI and EL. Our results include characterizations of the existence of FO-rewritings, tight complexity bounds for deciding whether an FO-rewriting exists (EXPTIME and PSPACE), and tight bounds on the (worst-case) size of FO-rewritings, when presented as a union of conjunctive queries.