Relational Perspective on Graph Query Languages

• Main Authors: Figueira, Diego, Lin, Anthony W, Peterfreund, Liat
• Format: Journal Article
• Language: English
• Published: 09-07-2024
• Subjects: Computer Science - Databases
• DOI: 10.48550/arxiv.2407.06766

We study a relational perspective of graph database querying. Such a
perspective underlies various graph database systems but very few theoretical
investigations have been conducted on it. This perspective offers a powerful
and unified framework to study graph database querying, by which algorithms and
complexity follow from classical results. We provide two concrete applications.
The first is querying property graphs. The property graph data model
supersedes previously proposed graph models and underlies the new standard GQL
for graph query languages. We show that this standard can be, by and large,
expressed by extensions of relational calculus with transitive closure
operators (FO[TC]) and existential second-order quantifiers (ESO). With this,
we obtain optimal data complexity bounds, along with extensions including
schema validation.
The second application is incorporating data from concrete domains (e.g.,
numbers) in graph database querying. We use embedded finite model theory and,
by exploiting a generic Restricted Quantifier Collapse (RQC) result for FO[TC]
and ESO, we obtain optimal data complexity bounds for GQL with arithmetics and
comparisons. Moreover, we show that Regular Data Path Querying with operations
on data (i.e. using register automata formalisms) can be captured in FO[TC]
over embedded finite graphs while preserving nondeterministic logspace data
complexity.