Conditional dependencies for horizontal decompositions
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A new decomposition theory for functional dependencies in the Relational Database Model is given. It uses a method to break up a relation into two subrelations whose union is the given relation. This horizontal decomposition is based on a new constraint: the conditional-functional dependency. It indicates how to decompose a relation into two restrictions of this relation. The only difference between the two subrelations is a functional dependency that holds in one subrelation but not in the other. Functional dependencies can be expressed as special conditional-functional dependencies.
The membership problem is solved for this new constraint, and also for another constraint, induced by the horizontal decomposition: the afunctional dependency.
An algorithm is described that performs the decomposition. It uses a new normal form: the Conditional Normal Form. The link between the horizontal- and the traditional vertical decomposition is explained.
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