Albert Atserias, Anuj Dawar, Phokion G. Kolaitis. On Preservation under Homomorphisms and Unions of Conjunctive Queries. In Alin Deutsch, editor, Proceedings of the Twenty-third ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, June 14-16, 2004, Paris, France. pages 319-329, ACM, 2004. [doi]
Abstract is missing.