1. Universal relation view; a pragmatic approach;Biskup,1983
2. System/U: a database system based on the universal relation assumption;Korth;ACM Trans. Database Syst.,1984
3. Toward logical data independence: a relational query language without relations;Maier,1982
4. Universal relation interfaces for database systems;Ulman,1983
5. Assumptions in relational database theory;Atzeni,1982