Database queries and constraints via lifting problems

Abstract

Previous work has demonstrated that categories are useful and expressive models for databases. In the current paper we build on that model, showing that certain queries and constraints correspond to lifting problems, as found in modern approaches to algebraic topology. In our formulation, each SPARQL graph pattern query corresponds to a category-theoretic lifting problem, whereby the set of solutions to the query is precisely the set of lifts. We interpret constraints within the same formalism, and then investigate some basic properties of queries and constraints. In particular, to any database π, we can associate a certain derived databaseQry(π) of queries on π. As an application, we explain how giving users access to certain parts ofQry(π), rather than direct access to π, improves the ability to manage the impact of schema evolution.