14.2. Predicate Specialization and Generalization

The previous section illustrated how the same UoD structure may be described by different, but equivalent, schemas and discussed the use of transformations to reshape one schema into another. This section considers a class of schema transformations known as predicate specialization, as well as its inverse, predicate generalization.

If two or more predicates may be thought of as special cases of a more general predicate, then we may replace them by the more general predicate, as long as the original distinction can be preserved in some way. For example, if we transform the schema of Figure 14.1(a) into that of Figure 14.1(b), we generalize smoking and drinking into indulging in a vice, where vice ...

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