1. Aho, A., J. Ullman, “Universality of Data Retrieval Languages”, Sixth ACM Symposium on Principles of Programming Languages, 1979.
2. Chandra, A. and Harel, D., “Computable Queries for Relational Data Bases”, JCSS 21, 156–178, 1980.
3. Chandra, A. and Harel, D., “Horn Clauses and the Fixpoint Query Hierarchy”, Proceedings First PODS, 1982.
4. Chandra, A. and Harel, D., “Structure and Complexity of Relational Queries”, JCSS 25, 99–128, 1982.
5. Chang, C., “On the Evaluation of Queries Containing Derived Relations in Relational Database”, in Advances in Data Base Theory Vol.1. H.Gallaire, J. Minker and J.M. Nicolas (eds.), Plenum Press, New York, pp 235–260, 1981.