Advanced processing for ontological queries
Proceedings of the VLDB Endowment
ICALP'11 Proceedings of the 38th international conference on Automata, languages and programming - Volume Part II
A logical toolbox for ontological reasoning
ACM SIGMOD Record
Highly acyclic groups, hypergraph covers, and the guarded fragment
Journal of the ACM (JACM)
Finite satisfiability for guarded fixpoint logic
Information Processing Letters
Datalog+/-: a family of languages for ontology querying
Datalog'10 Proceedings of the First international conference on Datalog Reloaded
FOSSACS'12 Proceedings of the 15th international conference on Foundations of Software Science and Computational Structures
A general Datalog-based framework for tractable query answering over ontologies
Web Semantics: Science, Services and Agents on the World Wide Web
Computing universal models under guarded TGDs
Proceedings of the 15th International Conference on Database Theory
Walking the complexity lines for generalized guarded existential rules
IJCAI'11 Proceedings of the Twenty-Second international joint conference on Artificial Intelligence - Volume Volume Two
On the complexity of ontological reasoning under disjunctive existential rules
MFCS'12 Proceedings of the 37th international conference on Mathematical Foundations of Computer Science
Towards more expressive ontology languages: The query answering problem
Artificial Intelligence
Disjunctive datalog with existential quantifiers: Semantics, decidability, and complexity issues
Theory and Practice of Logic Programming
Proceedings of the 32nd symposium on Principles of database systems
Querying the guarded fragment with transitivity
ICALP'13 Proceedings of the 40th international conference on Automata, Languages, and Programming - Volume Part II
The impact of disjunction on query answering under guarded-based existential rules
IJCAI'13 Proceedings of the Twenty-Third international joint conference on Artificial Intelligence
Taming the infinite chase: query answering under expressive relational constraints
Journal of Artificial Intelligence Research
Exact query reformulation over databases with first-order and description logics ontologies
Journal of Artificial Intelligence Research
Converging to the Chase -- A Tool for Finite Controllability
LICS '13 Proceedings of the 2013 28th Annual ACM/IEEE Symposium on Logic in Computer Science
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Evaluating a boolean conjunctive query q over a guarded first-order theory T is equivalent to checking whether (T \& not q) is unsatisfiable. This problem is relevant to the areas of database theory and description logic. Since q may not be guarded, well known results about the decidability, complexity, and finite-model property of the guarded fragment do not obviously carry over to conjunctive query answering over guarded theories, and had been left open in general. By investigating finite guarded bisimilar covers of hypergraphs and relational structures, and by substantially generalising Rosati's finite chase, we prove for guarded theories T and (unions of) conjunctive queries q that (i) T implies q iff T implies q over finite models, that is, iff q is true in each finite model of T and (ii) determining whether T implies q is {2EXPTIME}-complete. We further show the following results: (iii) the existence of polynomial-size conformal covers of arbitrary hypergraphs; (iv) a new proof of the finite model property of the clique-guarded fragment; (v) the small model property of the guarded fragment with optimal bounds; (vi) a polynomial-time solution to the canonisation problem modulo guarded bisimulation, which yields (vii) a capturing result for guarded-bisimulation-invariant PTIME.