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We demonstrate the power of object identities (oids) as a database query language primitive. We develop an object-based data model, whose structural part generalizes most of the known complex-object data models: cyclicity is allowed in both its schemas and instances. Our main contribution is the operational part of the data model, the query language IQL, which uses oids for three critical purposes: (1) to represent data-structures with sharing and cycles, (2) to manipulate sets, and (3) to express any computable database query. IQL can be type checked, can be evaluated bottom-up, and naturally generalizes most popular rule-based languages. The model can also be extended to incorporate type inheritance, without changes to IQL. Finally, we investigate an analogous value-based data model, whose structural part is founded on regular infinte trees and whose operational part is IQL.
Abiteboul et al. (Tue,) studied this question.