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Capturing Homomorphism-Closed Decidable Queries with Existential Rules

Camille Bourgaux 1 David Carral 2 Markus Krötzsch 3 Sebastian Rudolph 3 Michaël Thomazo 1 
1 VALDA - Value from Data
DI-ENS - Département d'informatique - ENS Paris, Inria de Paris
2 GRAPHIK - Graphs for Inferences on Knowledge
LIRMM - Laboratoire d'Informatique de Robotique et de Microélectronique de Montpellier, CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : Existential rules are a very popular ontology-mediated query language for which the chase represents a generic computational approach for query answering. It is straightforward that existential rule queries exhibiting chase termination are decidable and can only recognize properties that are preserved under homomorphisms. In this paper, we show the converse: every decidable query that is closed under homomorphism can be expressed by an existential rule set for which the standard chase universally terminates. Membership in this fragment is not decidable, but we show via a diagonalisation argument that this is unavoidable.
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Submitted on : Wednesday, September 15, 2021 - 4:40:47 PM
Last modification on : Friday, August 5, 2022 - 3:03:00 PM
Long-term archiving on: : Thursday, December 16, 2021 - 7:16:18 PM


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  • HAL Id : lirmm-03345614, version 1
  • ARXIV : 2107.07811


Camille Bourgaux, David Carral, Markus Krötzsch, Sebastian Rudolph, Michaël Thomazo. Capturing Homomorphism-Closed Decidable Queries with Existential Rules. KR 2021 - 18th International Conference on Principles of Knowledge Representation and Reasoning, Nov 2021, Virtual, Vietnam. pp.141--150. ⟨lirmm-03345614⟩



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