Re: Functional Dependencies > Uniqueness Constraints
- From: "Marshall" <marshall.spight@xxxxxxxxx>
- Date: 30 Aug 2006 16:21:41 -0700
paul c wrote:
Marshall wrote:
... (And of course there must be a rule that
says every base table must have at least one functional
dependency in which the union of the determinant set
and the dependent set equals the set of attributes. (This
restriction is sufficient to ensure every base table is a
relation; is it necessary?))
...
I would say not necessary. If a table is a representation of a
relation, then I`d think that even if no rule is stated, by definition
the union of the attributes is a CK, eg., if there is no stated
determinant set, all the attributes are in the dependent set. I can`t
think why one would want to state this, shouldn`t a dbms assume itÉ
Modulo the elsewhere-mentioned terminology issue, yes. The
way I usually think of it is that the system would reject a base
table declaration in which there was no key, but it is just as
valid to propose that the system would create a default one
containing all the attributes.
Marshall
.
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