Double Chain-Star: an RDF indexing scheme for fast processing of SPARQL joins

State of the art RDF stores often rely on exhaustive indexing and sequential (self-)joins for SPARQL query processing. However, query execution is dependent on, and often limited by the underlying storage and indexing schemes. Even though RDF can give birth to datasets with loosely defined schemas, it is common for an emerging structure to be present in the data. In this paper we introduce a novel indexing scheme, called Double Chain Star (DCS), that takes advantage of the inherent structure that is often found in RDF datasets by extending the notion of Characteristic Sets to cater for chain-star joins. DCS essentially reduces pairs of chain-star patterns that typically involve multiple self-joins, to mere index scans. We perform preliminary experiments and show promising results in comparison with Jena TDB and RDF-3X.