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The Availability of Domain/Key Normal Form
Abstract
In my earlier paper, “Understanding Functional Dependency” (2002), I distinguished intensional and extensional characterizations of functional and other dependencies used in defining the Normal Forms for relational databases. In that paper, I left incomplete my discussion of how this distinction applies to Domain/Key Normal Form (DK/NF). In this paper, I will continue that discussion. Extensional characteristics are those which remain the same through substitution of terms with the same reference, whereas intensional characteristics do not. In a database context, extensionality means that the only features of fields appealed to is the frequency of their appearance with other fields, with the same or different values. Meanings or connotations of field names or values, and connections between fields having to do with knowledge about the meanings or business rules or conventions connecting field values are intensional and therefore have no place in extensional database considerations. In my earlier paper (2002), I showed that the first three normal forms can be done on an extensional basis (and Boyce-Codd, fourth and fifth normal forms as well). Although many texts mention intensional elements in defining functional dependency, this is not necessary.
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