Richard C. H. Connor, David J. McNally, Ronald Morrison. Subtyping and Assignment in Database Programming Languages. In Paris C. Kanellakis, Joachim W. Schmidt, editors, Database Programming Languages: Bulk Types and Persistent Data. 3rd International Workshop, August 27-30, 1991, Nafplion, Greece, Proceedings. pages 363-382, Morgan Kaufmann, 1991. [doi]
Abstract is missing.