Re: Functional Dependencies > Uniqueness Constraints

paul c wrote:

Bob Badour wrote:

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

I think you have determinant and dependent reversed. The attributes of a candidate key are the determinant set, and the remaining attributes are each dependent attributes. Thus, if no other key is specified, all attributes are in the determinant set and the set of dependent attributes is empty.

What Marshall stated is an invariant of every relation for every candidate key. In fact, it seems to me Marshall's statement is just a restatement of candidate keys, but there could be subtleties I miss.

Right, I did reverse them, in the course of trying to use Marshall's lingo. Still if the dependent set stood for an RVA, maybe the reversal would be true in a sort-of way.

No. In that context, the relation value is no different from any other value.

[snipped the part I found confusing]
.

Relevant Pages

  • Re: Functional Dependencies > Uniqueness Constraints
    ... the union of the attributes is a CK, eg., if there is no stated ... determinant set, all the attributes are in the dependent set. ... candidate key are the determinant set, ...
    (comp.databases.theory)
  • Re: Functional Dependencies > Uniqueness Constraints
    ... the union of the attributes is a CK, eg., if there is no stated ... determinant set, all the attributes are in the dependent set. ... candidate key are the determinant set, ...
    (comp.databases.theory)
  • Re: Functional Dependencies > Uniqueness Constraints
    ... and the dependent set equals the set of attributes. ... 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. ... The attributes of a candidate key are the determinant set, and the remaining attributes are each dependent attributes. ...
    (comp.databases.theory)
  • Re: Functional Dependencies > Uniqueness Constraints
    ... and the dependent set equals the set of attributes. ... 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. ... The attributes of a candidate key are the determinant set, and the remaining attributes are each dependent attributes. ...
    (comp.databases.theory)
  • Re: Functional Dependencies > Uniqueness Constraints
    ... paul c wrote: ... the union of the attributes is a CK, eg., if there is no stated ... determinant set, all the attributes are in the dependent set. ...
    (comp.databases.theory)