Constrained Regular Expressions in SPARQL

نویسندگان

  • Faisal Alkhateeb
  • Jean-François Baget
  • Jérôme Euzenat
چکیده

RDF is a knowledge representation language dedicated to the annotation of resources within the Semantic Web. Though RDF itself can be used as a query language for an RDF knowledge base (using RDF consequence), the need for added expressivity in queries has led to the definition of the SPARQL query language. SPARQL queries are defined on top of graph patterns that are basically RDF (and more precisely GRDF) graphs. To be able to characterize paths of arbitrary length in a query (e.g., "does there exist a trip from town A to town B?"), we have already proposed the PRDF (for Path RDF) language, effectively mixing RDF reasonings with database-inspired regular paths. However, these queries do not allow expressing constraints on internal nodes (e.g., "Moreover, one of the stops must provide a wireless connection."). To express these constraints, we present here an extension of RDF, called CRDF (for Constrained paths RDF). For this extension of RDF, we provide an abstract syntax and an extension of RDF semantics. We characterize query answering (the query is a CRDF graph, the knowledge base is an RDF graph) as a case of CRDF entailment that can be computed using a particular of graph homomorphism. Finally, we use CRDF graphs to generalize SPARQL graph patterns, defining the CSPARQL extension of that query language, and prove that the problem of query answering using only CRDF graphs is an NP-hard problem. Key-words: semantic web, RDF, SPARQL, constrained regular expressions, graph homomorphism, paths, SPARQL extensions. in ria -0 01 88 28 7, v er si on 3 16 D ec 2 00 7 Expressions régulières contraintes dans SPARQL Rapport de recherche INRIA Résumé : RDF est un langage de représentation de connaissances dédié à l’annotation de ressources dans le cadre du web sémantique. Bien que RDF lui-même peut être utilisé comme un langage de requête pour une base de connaissances RDF (utilisant conséquence RDF), la nécessité d’ajouter expressivité dans les requêtes a conduit à la définition du langage de requête SPARQL. Les requêtes SPARQL sont définies au sommet des graphes patterns qui sont fondamentalement RDF (et plus précisément GRDF) graphes. Pour exprimer les chemins d’un longueur arbitraire dans une requête (e.g., "existe-t-il un chemin de la ville A à la ville B?"), Nous avons déjà proposé le langage PRDF (pour Path RDF). Cependant, les requêtes PRDF ne permettent pas d’exprimer des contraintes sur les nIJuds internes (e.g., "En outre, l’un des arrêts doit fournir une connexion sans fil."). Pour exprimer ces contraintes, nous présentons ici une extension de RDF, appelé CRDF (pour Constrained Path RDF). Pour cette extension de RDF, nous proposons une syntaxe abstraite et une extension de RDF sémantique. Nous caractérisons la réponse à la requête (la requête est un graphe CRDF, et la base de connaissances est un graphe RDF) comme un cas particulier de la conséquence CRDF qui peut être calculé en utilisant une sorte d’homomorphisme. Enfin, nous utilisons les graphes CRDF de généraliser SPARQL, en définissant l’extension CSPARQL de ce langage des requêtes, et de prouver que le problème de répondre à des requêtes en utilisant uniquement les graphes CRDF est un NP difficile problème. Mots-clés : web sémantique, RDF, SPARQL, expressions régulières contraintes, homomorphisme, chemins, extensions de SPARQL. in ria -0 01 88 28 7, v er si on 3 16 D ec 2 00 7 CSPARQL Query Language 3

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تاریخ انتشار 2008