1. A comparative study of abstract data type concepts;Bothe;Elektronische Informationsverarbeitung und Kybernetik,1981
2. Partial abstract types;Broy;Acta Inform,1982
3. Observability concepts in abstract data type specifications;Giarratana,1976
4. Products of automata and the problem of covering;Ginzburg;Trans. Amer. Math. Soc.,1965
5. Universal realization, persistent interconnection and implementation of abstract modules;Goguen,1982