1. Akahani J, Hiramatsu K, Satoh T (2003) Approximate query reformulation for multiple ontologies in the semantic web. NTT Tech Rev 1(2):83–87
2. Benslimane SM, Merazi A, Malki M, Bensaber DA (2008) Ontology mapping for querying heterogeneous information sources. INFOCOMP (J Comput Sci)
3. Imprialou M, Stoilos G, Grau BC (2012) Benchmarking ontology-based query rewriting systems. In: Twenty-sixth AAAI conference artificial intelligence, pp 779–785
4. Bikakis N, Gioldasis N, Tsinaraki C, Christodoulakis S (2009) Querying XML data with SPARQL. In: Proceedings of the 20th international conference on database and expert systems applications, pp 372–381
5. Cyganiak R (2005) A relational algebra for SPARQL. Technical Report http://www.hpl.hp.com/techreports/2005/HPL-2005-170.html , HP Laboratories Bristol