The design of a relational database system with abstract data types for domains
Sylvia L. Osborn, T. E. Heaven · ACM Transactions on Database Systems · 1986
An extension to the relational model is described in which domains can he arbitrarily defined as abstract data types. Operations on these data types include primitive operations, aggregates, and transformations. It is shown that these operations make the query language complete in the sense of Chandra and Harel. The system has been designed in such a way that new data types and their operations can be defined with a minimal amount of interaction with the database management system.