1. W3C. (2008, January 15). SPARQL Query Language for RDF. Retrieved June 1, 2012, from http://www.w3.org: http://www.w3.org/TR/rdf-sparql-query/.
2. Manola F, Miller E, McBride B. RDF primer, 2004[J]. 2014.
3. Cyganiak R. D2RQ-Accessing Relational Databases as Virtual RDF Graphs[J]. URL: http://d2rq. org/d2r-server (visited on 04/18/2014), 2012.
4. Seaborne, A. (2010, November). What is Jena? Retrieved June 1, 2012, from http://jena.apache.org/index.html.
5. Zviedris M, Barzdins G. ViziQuer: A Tool to Explore and Query SPARQL Endpoints.[C]//The Semanic Web: Research and Applications - 8th Extended Semantic Web Conference, ESWC 2011, Heraklion, Crete, Greece, May 29 - June 2, 2011, Proceedings, Part II. 2011:441-445.