Semantics and Optimization of the SPARQL 1.1 Federation Extension
The W3C SPARQL working group is defining the new SPARQL 1.1 query language. The SPARQL 1.1 focuses mainly on the description of the language. In this paper, the authors provide a formalization of the syntax and semantics of the SPARQL 1.1 federation extension, an important fragment of the language that has not yet received much attention. Besides, they propose optimization techniques for this fragment, provide an implementation of the fragment including these techniques, and carry out a series of experiments that show that their optimization procedures could significantly speed up the query evaluation process.