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Identifier 000414365
Title Optimizations for the query language SPARQL - LD
Alternative Title Βελτιστοποιήσεις για τη γλώσσα επερώτησης διασυνδεδεμένων δεδομένων SPARQL - LD
Author Γιαννάκης-Χαλβατζής, Αθανάσιος Ι.
Thesis advisor Τζίτζικας, Γιάννης
Reviewer Πλεξουσάκης, Δημήτρης
Φλουρής, Γεώργιος
Abstract Linked Data is a method for publishing structured data in the Web for assisting their linking and integration. A constantly increasing number of organizations and owners publish their data on the Web as Linked Data and SPARQL is the standard query language. However the majority of SPARQL implementations require the data to be available in advance in main memory or accessible through a SPARQL endpoint. SPARQL - LD is an extension of SPARQL 1. 1 (designed by FORTH - ICS) that overcomes this restriction and allows fetching and querying RDF data from any Web source and format i.e., RDFa, JSON - LD, Microdata and Microformats . Using SPARQL - LD, one can query a dataset corresponding to an RDF dump, or a dataset corresponding to the partial results of a query (i.e., discovered at query execution time), or RDF data that are dynamically created by Web Services. This functionality can motivate content owners to adopt the Linked Data principles and enrich the ir digital content and services with RDF, for having their data directly queryable via SPARQL – LD without having to create and maintain an operational SPARQL endpoint. In this thesis we focus on optimizations for SPARQL - LD, in particular on: (a) methods f or exploring the syntactic variations of graph patterns in a SPARQL query in order to choose a near to optimal execution plan without the use of statistics (to this end we utilize query reordering techniques, using selectivity estimation procedures on new unbound variables for increasing efficiency and decreasing intermediate results and thus the number of calls to remote sources), and (b) methods for parallelizing RDF data retrieval by using SPARQL - LD for efficient data caching. Finally, we report experi mental results on real datasets for evaluating the efficiency as well as the quality of the proposed optimizations. The results showed improved efficiency on SPARQL queries in comparison to existing methods
Language English
Subject Linked data
Semantic web
Σημασιολογικός ιστός
Issue date 2018-03-23
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Computer Science--Post-graduate theses
  Type of Work--Post-graduate theses
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