Abstract
There are two methods to handle redundancies caused by dependency constraints in relational databases. The first method, decomposition into relations in high-level normal form, has been studied by various authors, since it is very important for logical database design. The second method, representation by unnormalized form, is discussed in this paper. Although the latter method has not been studied except for simple cases, it is considered to be a very important tool for a user interface. We use four basic operations, GROUP-BY, ROW-NEST, COLUMN-NEST and RELATION-NEST to obtain unnormalized relations from a relation in a normal form. It is shown that 1. (1) functional dependencies can be handled by GROUP-BY operations, 2. (2) a join dependency is represented by a combination of GROUP-BY, ROW-NEST and RELATION-NEST operations and 3. (3) COLUMN-NEST operations can be used for a hierarchy of related attribute sets. Interactions among these operations are also discussed. We give procedures to represent an important class of constraints, consisting of one join dependency, functional dependencies satisfied by each component of the join dependency and a hierarchy of related attribute sets.
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