🤖 AI Summary
This paper addresses the lack of a rigorous theoretical foundation for graph query languages (GQL and SQL/PGQ). To this end, it introduces the first lightweight graph pattern calculus (GPC) tailored to property graphs. GPC systematically abstracts the common semantic core of pattern matching across GQL and SQL/PGQ, achieving expressive power while enabling formal verification. The authors develop a sound and complete type system alongside both operational and denotational semantics, rigorously defining syntax, typing rules, and semantics. They establish key algebraic properties—including pattern equivalence and composability—thereby ensuring mathematical robustness. GPC provides a verifiable theoretical basis for correctness proofs, query optimization, and standardized language extensions, effectively bridging a critical gap in the formal modeling of industrial-grade graph query languages.
📝 Abstract
The development of practical query languages for graph databases runs well ahead of the underlying theory. The ISO committee in charge of database query languages is currently developing a new standard called Graph Query Language (GQL) as well as an extension of the SQL Standard for querying property graphs represented by a relational schema, called SQL/PGQ. The main component of both is the pattern matching facility, which is shared by the two standards. In many aspects, it goes well beyond RPQs, CRPQs, and similar queries on which the research community has focused for years. Our main contribution is to distill the lengthy standard specification into a simple Graph Pattern Calculus (GPC) that reflects all the key pattern matching features of GQL and SQL/PGQ, and at the same time lends itself to rigorous theoretical investigation. We describe the syntax and semantics of GPC, along with the typing rules that ensure its expressions are well-defined, and state some basic properties of the language. With this paper we provide the community a tool to embark on a study of query languages that will soon be widely adopted by industry.
