Functional Dependency

Functional Dependencies

"From E/R Diagrams to Relational Designs" and "Converting Subclass Structures to Relations" showed us how to convert E/R designs into relational schemas. It is also possible for database designers to produce relational schemas directly from application requirements,

The Splitting/Combining Rule

Recall that in “Functional Dependencies” we defined the FD: A1A2…An → B1B2..Bm to be a shorthand for the set of FD's:

Third Normal Form

Sometimes, one encounters a relation schema and its FD's that are not in BCNF but that one doesn't want to decompose further. The following example is typical.

Multivalued Dependencies

A "multivalued dependency" is an assertion that two attributes or sets of attributes are independent of one another. This condition is, as we shall see, an overview of the notion of a functional dependency, in the sense that every FD implies a corresponding multivalued dependency.

Representing Set-Valued Attributes

Record structures are not the most complicated kind of attribute that can appear in ODL class definitions. Values can also be made using type constructors Set, Bag, List, Array, and Dictionary from Types in ODL. Each presents its own problems when migrating to the relational

Additional Constraint Examples

The same constraint notation permits us to express far more than referential integrity. For instance, we can express any functional dependency as an algebraic constraint, although the notation is more awkward than the FD notation introduced in Functional Dependencies.

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