Towards Equivalences for Federated SPARQL Queries

Abstract The most common way for exposing RDF data on theWeb is by means of SPARQL endpoints. These endpoints are Web services that implement the SPARQL protocol and then allow end users and applications to query just the RDF data they want. However the servers hosting the SPARQL endpoints re-strict the access to the data by limiting the amount of results returned by user queries or the amount of queries per time and client that can be issued. For ad-dressing this problem we analysed different alternatives that shall allow to obtain complete query result sets from the SPARQL endpoints by rewriting the origi-nal query using SPARQL1.1’s federated query extension. We show that some of the commonly used SPARQL query patterns for this task provide unsound re-sults while other patterns are more suitable for this task. We provide equivalent query patterns that help users in obtaining complete result sets circumventing the limitations imposed by servers.