[SCL] Functional dependencies

[John F. Sowa]

Chris,

A functional dependency does not *add* anything to a
relation.  It recognizes a feature that is already present.

CM>I don't see how they add anything to the notion of a
> relation.  Can you explain?

In database theory, the idea of a functional dependency
in a relation is extremely useful.  If you know that some
subset of arguments uniquely determine all the rest, that
subset can be used as a _key_ for indexing the relation.

Although it doesn't add anything in principle, the recognition
can be very useful in practice.  That is also true, by the 
way, of ordinary functions:  you don't *need* to distinguish
functions from other relations, but they make it possible to
optimize many kinds of inferences.

Bottom line:  Theoretically, it's a frill, but many people
who use CGs have found it useful.  But it can be added to CGs
without requiring anything special in CL syntax or semantics.

John