Chapter 12. K
key A candidate key, q.v. (unless the context demands otherwise).
key attribute An attribute of a given relvar that's part of at least one key of that relvar. See also subkey.
key constraint A constraint to the effect that a given subset of the heading of a given relvar is a key for that relvar. In Tutorial D, such a constraint is defined by means of a KEY specification within the pertinent relvar definition (see, e.g., the definitions for relvars S, P, and SP in the introduction to this dictionary). Note, however, that while the system will certainly enforce the uniqueness property implied by such a constraintsee candidate keyit can't in general enforce the corresponding irreducibility property as well. In other words, specifying ...
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