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As a generalization of inclusion dependencies that are found in relational databases, word constraints have been studied for semistructured data  as well as for an object-oriented model . In both contexts, it is assumed that each data entity has a unique identity, and two entities are equal if and only if they have the same identify. In this setting the decidability of the implication and finite implication problems for word constraints has been established. A question left open is whether these problems are still decidable in the context of an object-oriented model M≈ which supports complex values with nested structures and complex value equality. This paper provides an answer to that question. We characterize a schema in M≈ in terms of a type constraint and an equality constraint, and investigate the interaction between these constraints and word constraints. We show that in the presence of equality and type constraint, the implication and finite implication problems for word constraints are also decidable by giving a small model argument.
Peter Buneman, Wenfei Fan, and Scott Weinstein, "Equality, Type and Word Constraints", . September 1998.
Date Posted: 30 October 2006