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Existential Rules: A Graph-Based View

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Part of the Lecture Notes in Computer Science book series (LNISA,volume 7494)

Introduction

We consider rules that allow to assert the existence of new individuals, an ability called value invention in databases [AHV95]. These rules are of the form bodyhead, where the body and the head are function-free conjunctions of atoms, and variables that occur only in the head are existentially quantified, hence their name ∀ ∃-rules in [BLMS09, BLM10] or existential rules in [BMRT11, KR11]. Existential rules have long been studied in databases as high-level constraints called tuple generating dependencies (TGDs) [BV84]. Recently, there has been renewed interest for these rules in the context of ontology-based data access (OBDA), a new paradigm that seeks to exploit the semantics encoded in ontologies while querying data. The deductive database language Datalog could be seen as a natural candidate for expressing ontological knowledge in this context, however its limitation is that it does not allow for value invention, since all variables in a rule head necessarily occur in the rule body. Value invention has been recognized as a necessary prerequisite in an open-world perspective, where all individuals are not known a priori. It is in particular a feature of description logics (DLs), well-known languages dedicated to ontological representation and reasoning. This prerequisite motivated the recent extension of Datalog to existential rules, which gave rise to the Datalog +/- formalism [CGK08, CGL09].

Keywords

  • Description Logic
  • Conjunctive Query
  • Conceptual Graph
  • Query Answering
  • Existential Variable

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Mugnier, ML. (2012). Existential Rules: A Graph-Based View. In: Barceló, P., Pichler, R. (eds) Datalog in Academia and Industry. Datalog 2.0 2012. Lecture Notes in Computer Science, vol 7494. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-32925-8_3

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  • DOI: https://doi.org/10.1007/978-3-642-32925-8_3

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-642-32924-1

  • Online ISBN: 978-3-642-32925-8

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