Database Constraints And Homomorphism Dualities

Global-as-view (GAV) constraints form a class of database constraints that has been widely used in the study of data exchange and data integration. Specifically, relationships between different database schemas are commonly described by a schema mapping consisting of a finite set of GAV constraints. Such schema mappings can be viewed as representations of an infinite set of data examples. We study the following problem: when is finite set of GAV constraints uniquely characterizable via a finite set of data examples? By establishing a tight connection between this problem and homomorphism dualities, we obtain a simple criterion for unique characterizability. We also pinpoint the computational complexity of the corresponding decision problem.