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- 259 creator claudio-gutierrez.
- 259 creator jorge-a-perez.
- 259 creator marcelo-arenas.
- 259 type InProceedings.
- 259 label "nSPARQL: A Navigational Language for RDF".
- 259 sameAs 259.
- 259 abstract "It has been largely recognized that navigational capabilities are fundamental for graph databases query languages. However, although RDF is a directed labeled graph data format, the W3C Recommendation query language for RDF, SPARQL, only provides limited navigational functionalities. This has motivated several authors to propose extensions of SPARQL, or alternative query languages, that offer functionalities for navigating RDF data. In particular, we argued in [6] that nested regular expressions are appropriate to overcome this limitation, and we proposed a query language called nSPARQL that extends SPARQL with this type of expressions. In this paper, we continue with the investigation of nSPARQL. First, we show that nested regular expressions can be evaluated efficiently; if the appropriate data structure is used to store RDF graphs, then the evaluation of a nested regular expression E over an RDF graph G can be computed in time O(|G|*|E|). Second, as RDF graphs may contain RDFS vocabulary, we study how the navigational capabilities of nSPARQL can be used to evaluate queries according to the predefined semantics of RDFS. Evaluating queries which involve the RDFS vocabulary is challenging, and there is not yet consensus in the Semantic Web community on how to define a query language for RDFS. In this respect, we show that nSPARQL is expressive enough to answer SPARQL queries involving RDFS vocabulary by directly traversing the input RDF graphs. Moreover, we also prove that nesting is necessary to obtain this result. Namely, we show that, in general, regular expressions alone cannot be used to obtain the answer of a SPARQL query involving RDFS vocabulary.".
- 259 hasAuthorList authorList.
- 259 hasTopic Semantic_Web.
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- 259 keyword "RDF".
- 259 keyword "RDFS".
- 259 keyword "SPARQL".
- 259 keyword "navigating RDF data".
- 259 keyword "regular expressions".
- 259 title "nSPARQL: A Navigational Language for RDF".
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- 260 creator achille-fokoue.
- 260 creator aditya-kalyanpur.
- 260 creator edith-schonberg.
- 260 creator julian-dolby.
- 260 creator kavitha-srinivas.
- 260 creator li-ma.
- 260 creator xingzhi-sun.
- 260 type InProceedings.
- 260 label "Scalable Conjunctive Query Evaluation Over Large and Expressive Knowledge Bases".
- 260 sameAs 260.
- 260 abstract "Conjunctive query answering over OWL-DL ontologies is intractable in the worst case, but we present novel techniques which allow for efficient querying of large expressive knowledge bases in secondary storage. In particular, we show that we can effectively answer conjunctive queries without building a complete completion forest for a large ABox (unlike state of the art tableau reasoners). Instead we rely on the completion forest of a dramatically reduced summary of the Abox. We demonstrate the effectiveness of this approach in Aboxes with up to 45 million assertions.".
- 260 hasAuthorList authorList.
- 260 hasTopic Semantic_Web.
- 260 isPartOf proceedings.
- 260 keyword "Conjunctive query".
- 260 keyword "OWL Reasoning".
- 260 keyword "Ontologies".
- 260 keyword "Scalability".
- 260 title "Scalable Conjunctive Query Evaluation Over Large and Expressive Knowledge Bases".
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- 262 creator claudio-gutierrez.
- 262 creator renzo-angles.
- 262 type InProceedings.
- 262 label "The Expressive Power of SPARQL".