arXiv subjects

Jose-Emilio Labra-Gayo

Publications and source records attributed to Jose-Emilio Labra-Gayo.

3 recordsLinked to original sources

arXiv2026

sheval: An RDF data shapes evaluation tool and test-suite for recursive shapes

Two different languages have been developed to validate RDF data based on the concept of a shape: ShEx and SHACL. In each language it is possible to define a shape that refers to itself, which is called a recursive shape. While in the case of ShEx, the semantics of recursive shapes is well defined and is part of the specification, in the case of SHACL, the semantics of recursive shapes is left to the implementation of the different SHACL engines. Consequently, the different SHACL engines show different behaviours when confronted with recursive shapes. In this paper we present sheval: an evaluation framework consisting of a tool and a test suite that can be used to compare the behaviour of different shapes technologies when confronted with recursive definitions. The tool has been used to evaluate and understand the differences in the implementation of recursive shapes in ShEx and SHACL. It provides a framework for testing and comparing the behaviour of different shape engines, helping to identify inconsistencies and potential issues, and providing a basis for further research and development in the field of shape-based validation of RDF data.

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arXiv2026

Common Foundations for Recursive Shape Languages

As schema languages for RDF data become more mature, we are seeing efforts to extend them with recursive semantics, applying diverse ideas from logic programming and description logics. While ShEx has an official recursive semantics based on greatest fixpoints (GFP), the discussion for SHACL is ongoing and seems to be converging towards least fixpoints (LFP). A practical study we perform shows that, indeed, ShEx validators implement GFP, whereas SHACL validators are more heterogeneous. This situation creates tension between ShEx and SHACL, as their semantic commitments appear to diverge, potentially undermining interoperability and predictability. We aim to clarify this design space by comparing the main semantic options in a principled yet accessible way, hoping to engage both theoreticians and practitioners, especially those involved in developing tools and standards. We present a unifying formal semantics that treats LFP, GFP, and supported model semantics (SMS), clarifying their relationships and highlighting a duality between LFP and GFP on stratified fragments. Next, we investigate to which extent the directions taken by SHACL and ShEx are compatible. We show that, although ShEx and SHACL seem to be going in different directions, they include large fragments with identical expressive power. Moreover, there is a strong correspondence between these fragments through the aforementioned principle of duality. Finally, we present a complete picture of the data and combined complexity of ShEx and SHACL validation under LFP, GFP, and SMS, showing that SMS comes at a higher computational cost under standard complexity-theoretic assumptions.

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arXiv2017

Validating and describing linked data portals using shapes

Linked data portals need to be able to advertise and describe the structure of their content. A sufficiently expressive and intuitive schema language will allow portals to communicate these structures. Validation tools will aid in the publication and maintenance of linked data and increase their quality. Two schema language proposals have recently emerged for describing the structures of RDF graphs: Shape Expressions (ShEx) and Shapes Constraint Language (SHACL). In this paper we describe how these formalisms can be used in the development of a linked data portal to describe and validate its contents. As a use case, we specify a data model inspired by the WebIndex data model, a medium size linked data portal, using both ShEx and SHACL, and we propose a benchmark that can generate compliant test data structures of any size. We then perform some preliminary experiments showing performance of one validation engine based on ShEx.

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