document: SPARQ2L : towards support for subgraph extraction queries in rdf databases Many applications in analytical domains often have the need to `` connect the dots '' i.e. , query about the structure of data . In bioinformatics for example , it is typical to want to query about interactions between proteins . The aim of such queries is to `` extract '' relationships between entities i.e. paths from a data graph . Often , such queries will specify certain constraints that qualifying results must satisfy e.g. paths involving a set of mandatory nodes . Unfortunately , most present day Semantic Web query languages including the current draft of the anticipated recommendation SPARQL , lack the ability to express queries about arbitrary path structures in data . In addition , many systems that support some limited form of path queries rely on main memory graph algorithms limiting their applicability to very large scale graphs . In this paper , we present an approach for supporting Path Extraction queries . Our proposal comprises ( i ) a query language SPARQ2L which extends SPARQL with path variables and path variable constraint expressions , and ( ii ) a novel query evaluation framework based on efficient algebraic techniques for solving path problems which allows for path queries to be efficiently evaluated on disk resident RDF graphs . The effectiveness of our proposal is demonstrated by a performance evaluation of our approach on both real world based and synthetic dataset .
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