nSPARQL: A Navigational Language for RDF

Navigational features have been largely recognized as fundamental for graph database query languages. This fact has motivated several authors to propose RDF query languages with navigational capabilities. In particular, we have argued in a previous paper that nested regular expressions are appropriate to navigate RDF data, and we have proposed the nSPARQL query language for RDF, that uses nested regular expressions as building blocks. In this paper, we study some of the fundamental properties of nSPARQL concerning expressiveness and complexity of evaluation. Regarding expressiveness, we show that nSPARQL is expressive enough to answer queries considering the semantics of the RDFS vocabulary by directly traversing the input graph. We also show that nesting is necessary to obtain this last result, and we study the expressiveness of the combination of nested regular expressions and SPARQL operators. Regarding complexity of evaluation, we prove that the evaluation of a nested regular expression E over an RDF graph G can be computed in time O (|G |·|E |).

[1]  Vassilis Christophides,et al.  RQL: a declarative query language for RDF , 2002, WWW.

[2]  Bernhard Beckert,et al.  Dynamic Logic , 2007, The KeY Approach.

[3]  Alberto O. Mendelzon,et al.  Foundations of semantic web databases , 2004, PODS.

[4]  Neil Immerman,et al.  Reachability Logic: An Efficient Fragment of Transitive Closure Logic , 2000, Log. J. IGPL.

[5]  Jorge Pérez,et al.  Minimal Deductive Systems for RDF , 2007, ESWC.

[6]  Claudio Gutierrez,et al.  Survey of graph database models , 2008, CSUR.

[7]  Marcelo Arenas,et al.  An Extension of SPARQL for RDFS , 2008, SWDB-ODBIS.

[8]  Alberto O. Mendelzon,et al.  Finding Regular Simple Paths in Graph Databases , 1989, SIAM J. Comput..

[9]  Marcelo Arenas,et al.  Semantics and Complexity of SPARQL , 2006, International Semantic Web Conference.

[10]  Amit P. Sheth,et al.  SPARQ2L: towards support for subgraph extraction queries in rdf databases , 2007, WWW '07.

[11]  Frank van Harmelen,et al.  Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema , 2002, SEMWEB.

[12]  Jean-François Baget,et al.  RDF with regular expressions , 2006 .

[13]  Jean-François Baget,et al.  Extending SPARQL with regular expression patterns (for querying RDF) , 2009, J. Web Semant..

[14]  Marcelo Arenas,et al.  nSPARQL: A navigational language for RDF , 2010, J. Web Semant..

[15]  Nicholas Gibbins,et al.  3store: Efficient Bulk RDF Storage , 2003, PSSS.

[16]  Stephan Merz,et al.  Model Checking , 2000 .

[17]  Faisal Alkhateeb,et al.  Querying RDF(S) with Regular Expressions , 2008 .

[18]  Dan Brickley,et al.  Rdf vocabulary description language 1.0 : Rdf schema , 2004 .

[19]  Steven J. DeRose,et al.  XML Path Language (XPath) , 1999 .

[20]  Tim Furche,et al.  RDF Querying: Language Constructs and Evaluation Methods Compared , 2006, Reasoning Web.

[21]  Maarten Marx,et al.  Conditional XPath , 2005, TODS.

[22]  Jean-François Baget,et al.  Constrained Regular Expressions in SPARQL , 2008, SWWS.

[23]  Ashok K. Chandra,et al.  Optimal implementation of conjunctive queries in relational data bases , 1977, STOC '77.

[24]  Krys J. Kochut,et al.  SPARQLeR: Extended Sparql for Semantic Association Discovery , 2007, ESWC.

[25]  Moshe Y. Vardi.  The complexity of relational query languages (Extended Abstract) , 1982, STOC '82.