We propose a formal semantics for object data models. Our approach may be seen as a semantic approach to object-relational models. It is object-oriented because it captures the main concepts of object-oriented models namely: class, method, object identity, inheritance, collection types and prersistence; it is relational because it maintain the main characteristics of the relational model, especially the clear separation between schema, instance and querying. Moreover, it is functional in the senes that it is based on a simple algebra of partial functions whose main role is to perform arithmetic computations, similar to commerical languages. Another important aspect of our approach is that it provides a rigorous mathematical treatment of null value.
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