RDFGraphGen: An RDF Graph Generator based on SHACL Shapes

Developing and testing modern RDF-based applications often requires access to RDF datasets with certain characteristics. Unfortunately, it is very difficult to publicly find domain-specific knowledge graphs that conform to a particular set of characteristics. Hence, in this paper we propose RDFGraphGen, an open-source RDF graph generator that uses characteristics provided in the form of SHACL (Shapes Constraint Language) shapes to generate synthetic RDF graphs. RDFGraphGen is domain-agnostic, with configurable graph structure, value constraints, and distributions. It also comes with a number of predefined values for popular schema.org classes and properties, for more realistic graphs. Our results show that RDFGraphGen is scalable and can generate small, medium, and large RDF graphs in any domain.Comment: 11 pages, 2 figure

Expressiveness of SHACL Features

SHACL is a W3C-proposed schema language for expressing structural constraints on RDF graphs. Recent work on formalizing this language has revealed a striking relationship to description logics. SHACL expressions can use four fundamental features that are not so common in description logics. These features are zero-or-one path expressions; equality tests; disjointness tests; and closure constraints. Moreover, SHACL is peculiar in allowing only a restricted form of expressions (so-called targets) on the left-hand side of inclusion constraints. The goal of this paper is to obtain a clear picture of the impact and expressiveness of these features and restrictions. We show that each of the four features is primitive: using the feature, one can express boolean queries that are not expressible without using the feature. We also show that the restriction that SHACL imposes on allowed targets is inessential, as long as closure constraints are not used

Expressiveness of SHACL Features and Extensions for Full Equality and Disjointness Tests

SHACL is a W3C-proposed schema language for expressing structural constraints on RDF graphs. Recent work on formalizing this language has revealed a striking relationship to description logics. SHACL expressions can use three fundamental features that are not so common in description logics. These features are equality tests; disjointness tests; and closure constraints. Moreover, SHACL is peculiar in allowing only a restricted form of expressions (so-called targets) on the left-hand side of inclusion constraints. The goal of this paper is to obtain a clear picture of the impact and expressiveness of these features and restrictions. We show that each of the four features is primitive: using the feature, one can express boolean queries that are not expressible without using the feature. We also show that the restriction that SHACL imposes on allowed targets is inessential, as long as closure constraints are not used. In addition, we show that enriching SHACL with "full" versions of equality tests, or disjointness tests, results in a strictly more powerful language

MaximeJakubowski/SRR: Release for general use

<p>Release for general use with doi.</p&gt

Shapes Constraint Language: Formalization, Expressiveness, and Provenance

The Shapes Constraint Language (SHACL) is a W3C-proposed schema language for expressing structural constraints on RDF graphs. Constraints on nodes are called “shapes”, and when shapes are coupled with so-called “target declarations”, specifying which nodes need to adhere to which shapes, we have a complete constraint on RDF graphs. We study several aspects of this language. First, recent formalizations show a striking resemblance with description logics. We build on top of these formalizations to come to an understanding of SHACL as a logic. Furthermore, because the SHACL specification only defines semantics for non-recursive SHACL, some efforts have been made to allow recursive SHACL schemas. We argue that for defining and studying semantics of recursive SHACL, lessons can be learned from research in non-monotonic reasoning. We look at the proposed semantics from the literature and compare it with techniques from well-established research from non-monotonic reasoning. Next, SHACL expressions can use three fundamental features that are not so common in similar logics. These features are equality tests; disjointness tests; and closure constraints. It is not clear how the presence of these non-standard features impacts the expressiveness of SHACL. We show that each of the three features is primitive: using the feature, one can express boolean queries that are not expressible without using the feature. We also show that the restriction that SHACL imposes on allowed targets is inessential, as long as closure constraints are not used. In addition, we show that enriching SHACL with “full” versions of equality tests, or disjointness tests, results in a strictly more powerful language. Lastly, we propose provenance semantics for SHACL. We propose the notion of neighborhood of a node v satisfying a given shape in a graph G. This neighborhood is a subgraph of G, and provides data provenance of v for the given shape. We establish a correctness property for the obtained provenance mechanism, by proving that neighborhoods adhere to the Sufficiency requirement articulated for provenance semantics for database queries. As an additional benefit, neighborhoods allow a novel use of shapes: the extraction of a subgraph from an RDF graph, the so-called shape fragment. We compare shape fragments with SPARQL queries. We discuss implementation strategies for computing neighborhoods, and present initial experiments demonstrating that our ideas are feasible

MaximeJakubowski/sls_project: First release

<p>First release for general use.</p&gt

Compiling SHACL Into SQL

Constraints on graph data expressed in the Shapes Constraint Language (SHACL) can be quite complex. This brings the challenge of efficient validation of complex SHACL constraints on graph data. This challenge is remarkably similar to the processing of analytical queries, investigated intensively in the database community. Motivated by this observation, we have devised an efficient compilation technique from SHACL into SQL, under a natural relational representation of RDF graphs. Our conclusion is that the powerful processing and optimization techniques, already offered by modern SQL engines, are more than up to the challenge

SHACL: A description logic in disguise

SHACL is a W3C-proposed language for expressing structural constraints on RDF graphs. In recent years, SHACL's popularity has risen quickly. This rise in popularity comes with questions related to its place in the semantic web, particularly about its relation to OWL (the de facto standard for expressing ontological information on the web) and description logics (which form the formal foundations of OWL). We answer these questions by arguing that SHACL is in fact a description logic. On the one hand, our answer is surprisingly simple, some might even say obvious. But, on the other hand, our answer is also controversial. By resolving this issue once and for all, we establish the field of description logics as the solid formal foundations of SHACL