A Relational Algebra for Complex Objects Based on Partial Information
نویسنده
چکیده
We study an approach to relational databases which treats relations not as subsets of a Cartesian product but as subsets of some domain { a partially ordered space of descriptions. This approach permits generalizations of relations that admit null values and variants. In previous work it was shown how to deene the notion of a relation scheme in such a setting. Here we provide a characterization of a scheme that is more general, and show that operations analogous to projection, selection and join retain the desired properties. Schemes also allow us to develop dependency theory for such generalized relations. An extension of this model is described which admits a set constructor and is therefore useful for the study of higher-order relations and their generalizations.
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