Shape Fragments

TL;DR

This paper introduces shape fragments, a novel method using SHACL shapes to extract subgraphs from RDF graphs, with formal definitions, correctness proofs, comparisons to SPARQL, implementation options, and initial experiments.

Contribution

It proposes a new shape fragment mechanism for RDF graph extraction using SHACL, extending the Linked Data Fragments framework with formalization and initial validation.

Findings

Shape fragments can be formally defined and related to provenance.

Shape fragments are comparable to SPARQL queries in functionality.

Initial experiments show shape fragments are feasible and practical.

Abstract

In constraint languages for RDF graphs, such as ShEx and SHACL, constraints on nodes and their properties in RDF graphs are known as "shapes". Schemas in these languages list the various shapes that certain targeted nodes must satisfy for the graph to conform to the schema. Using SHACL, we propose in this paper a novel use of shapes, by which a set of shapes is used to extract a subgraph from an RDF graph, the so-called shape fragment. Our proposed mechanism fits in the framework of Linked Data Fragments. In this paper, (i) we define our extraction mechanism formally, building on recently proposed SHACL formalizations; (ii) we establish correctness properties, which relate shape fragments to notions of provenance for database queries; (iii) we compare shape fragments with SPARQL queries; (iv) we discuss implementation options; and (v) we present initial experiments demonstrating that shape fragments are a feasible new idea.