Balloon Fusion: SPARQL rewriting based on unified co-reference information

While Linked Open Data showed enormous increase in volume, yet there is no single point of access for querying the over 200 SPARQL repositories. In this paper we present Balloon Fusion, a SPARQL 1.1 rewriting and query federation service build on crawling and consolidating co-reference relationships in over 100 reachable Linked Data SPARQL Endpoints. The results of this process are 17.6M co-reference statements that have been clustered to 8.4M distinct semantic entities and are now accessible as download for further analysis. The proposed SPARQL rewriting performs a substitution of all URI occurrences with their synonyms combined with an automatic endpoint selection based on URI origin for a comprehensive query federation. While we show the technical feasibility, we also critically reflect the current status of the Linked Open Data cloud: although it is huge in size, access via SPARQL Endpoints is complicated in most cases due to missing quality of service.