Context-Free Path Queries on RDF Graphs

TL;DR

This paper introduces cfSPARQL, an extension of SPARQL that incorporates context-free grammars, enabling more expressive navigational graph queries over RDF graphs while maintaining efficient evaluation.

Contribution

It presents cfSPARQL, the first extension of SPARQL with context-free grammars, increasing expressivity beyond regular expressions in graph querying.

Findings

cfSPARQL is more expressive than property paths.

It can model complex graph relations like similarities and alignments.

Evaluation remains computationally efficient.

Abstract

Navigational graph queries are an important class of queries that canextract implicit binary relations over the nodes of input graphs. Most of the navigational query languages used in the RDF community, e.g. property paths in W3C SPARQL 1.1 and nested regular expressions in nSPARQL, are based on the regular expressions. It is known that regular expressions have limited expressivity; for instance, some natural queries, like same generation-queries, are not expressible with regular expressions. To overcome this limitation, in this paper, we present cfSPARQL, an extension of SPARQL query language equipped with context-free grammars. The cfSPARQL language is strictly more expressive than property paths and nested expressions. The additional expressivity can be used for modelling graph similarities, graph summarization and ontology alignment. Despite the increasing expressivity, we show that cfSPARQL still enjoys a low computational complexity and can be evaluated efficiently.