1. Further normalization of database sublanguages;Codd,1970
2. Design and implementation of relational database systems;Pangalos,1980
3. Conceptual database schema design;Pangalos;Inf. Age,1986
4. Design of integrated hospital databases;Pangalos;Medical Informatics,1986
5. ISO/TR 9007, concepts and terminology for the conceptual schema and the information base,1987