Computer Science and Engineering, Department of


Date of this Version



D. Srivastava, R. Ramakrishnan, P. Z. Revesz, Constraint objects, Proc. Workshop on Principles and Practice of Constraint Programming, Springer LNCS 874, pp. 218--228, Orcas Island, Washington, USA, May 1994.


We describe the Constraint Object Data Model (CODM), which enhances an object-based data model with existential constraints to naturally represent partially specified information. We present the Constraint Object Query Language (COQL), a declarative, rule-based query language that can be used to infer relationships about and monotonically refine information represented in the CODM. COQL has a model-theoretic and an equivalent fixed-point semantics, based on the notions of constraint entailment and "proofs in all possible worlds." We also provide a novel polynomial-time algorithm for quantifier elimination for set-order constraints, a restricted class of set constraints that uses membership of subset-equal.