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Static analysis of semantic web queries with ShEx schema constraints

Abstract : Data structured in the Resource Description Framework (RDF) are increasingly available in large volumes. This leads to a major need and research interest in novel methods for query analysis and compilation for making the most of RDF data extraction. SPARQL is the widely used and well supported standard query language for RDF data. In parallel to query language evolutions, schema languages for expressing constraints on RDF datasets also evolve. Shape Expressions (ShEx) are increasingly used to validate RDF data, and to communicate expected graph patterns. Schemas in general are important for static analysis tasks such as query optimisation and containment. Our purpose is to investigate the means and methodologies for SPARQL query static analysis and optimisation in the presence of ShEx schema constraints.Our contribution is mainly divided into two parts. In the first part we consider the problem of SPARQL query containment in the presence of ShEx constraints. We propose a sound and complete procedure for the problem of containment with ShEx, considering several SPARQL fragments. Particularly our procedure considers OPTIONAL query patterns, that turns out to be an important feature to be studied with schemas. We provide complexity bounds for the containment problem with respect to the language fragments considered. We also propose alternative method for SPARQL query containment with ShEx by reduction into First Order Logic satisfiability, which allows for considering SPARQL fragment extension in comparison to the first method. This is the first work addressing SPARQL query containment in the presence of ShEx constraints.In the second part of our contribution we propose an analysis method to optimise the evaluation of conjunctive SPARQL queries, on RDF graphs, by taking advantage of ShEx constraints. The optimisation is based on computing and assigning ranks to query triple patterns, dictating their order of execution. The presence of intermediate joins between the query triple patterns is the reason why ordering is important in increasing efficiency. We define a set of well-formed ShEx schemas, that possess interesting characteristics for SPARQL query optimisation. We then develop our optimisation method by exploiting information extracted from a ShEx schema. We finally report on evaluation results performed showing the advantages of applying our optimisation on the top of an existing state-of-the-art query evaluation system.
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Abdullah Abbas. Static analysis of semantic web queries with ShEx schema constraints. Web. Université Grenoble Alpes, 2017. English. ⟨NNT : 2017GREAM064⟩. ⟨tel-01865547⟩

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