A proposal for an interchange abstract syntax for (parallel) Prolog

We propose an abstract syntax for Prolog that will help the manipulation of programs at compile-time, as well as the exchange of sources and information among the tools designed for this manipulation. This includes analysers, partial evaluators, and program transformation tools. We have chosen to concentrate on the information exchange format, rather than on the syntax of programs, for which we assume a simplified format. Our purpose is to provide a low-level meeting point for the tools which will allow them to read the same programs and understand the information about them. This report describes our first design in an informal way. We expect this design to evolve and concretize, along with the future development of the tools, during the project.

Federating queries in SPARQL 1.1: syntax, semantics and evaluation

Given the sustained growth that we are experiencing in the number of SPARQL endpoints available, the need to be able to send federated SPARQL queries across these has also grown. To address this use case, the W3C SPARQL working group is defining a federation extension for SPARQL 1.1 which allows for combining graph patterns that can be evaluated over several endpoints within a single query. In this paper, we describe the syntax of that extension and formalize its semantics. Additionally, we describe how a query evaluation system can be implemented for that federation extension, describing some static optimization techniques and reusing a query engine used for data-intensive science, so as to deal with large amounts of intermediate and final results. Finally we carry out a series of experiments that show that our optimizations speed up the federated query evaluation process.