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The current schema design theories assume that a database may be regarded as a single relation. From the practical point of view, this is hardly acceptable. However, if a relation is allowed to have u...nspecified items, any database can be represented as a partial relation. Since the normalization theory is defined with respect to relations, it needs to be extended so that it may become applicable to partial relations. As extensions of dependencies, natural dependencies are defined. They are axiomatized, and the set of axioms is proved its completeness. The schema design based on natural dependencies solves not only the problems caused by a universal relation assumption but also the update anomalies caused by decomposition of a database.続きを見る
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