Common Foundations for SHACL, ShEx, and PG-Schema

TL;DR

This paper provides a formal comparison of SHACL, ShEx, and PG-Schema, three graph schema languages, highlighting their commonalities and differences to aid understanding and interoperability.

Contribution

It introduces a unified framework to formally define and compare the core components of these schema languages, revealing their shared functionalities and unique features.

Findings

Identifies core commonalities among the schema languages.

Highlights distinctive features of each language.

Provides formal definitions to facilitate comparison.

Abstract

Graphs have emerged as an important foundation for a variety of applications, including capturing and reasoning over factual knowledge, semantic data integration, social networks, and providing factual knowledge for machine learning algorithms. To formalise certain properties of the data and to ensure data quality, there is a need to describe the schema of such graphs. Because of the breadth of applications and availability of different data models, such as RDF and property graphs, both the Semantic Web and the database community have independently developed graph schema languages: SHACL, ShEx, and PG-Schema. Each language has its unique approach to defining constraints and validating graph data, leaving potential users in the dark about their commonalities and differences. In this paper, we provide formal, concise definitions of the core components of each of these schema languages. We employ a uniform framework to facilitate a comprehensive comparison between the languages and identify a common set of functionalities, shedding light on both overlapping and distinctive features of the three languages.