Re: Key attributes with list values was Re: What are the differences ...KEY

If an entity has more than one candidate key, and if successive database states contain elements that are identical except for the value of only one of those candidate keys, do those elements represent the same entity?

Are you implying that temporal constraints are irrelevant?

I submit that it is not possible to enforce a temporal constraint in a relational database without tossing the concept of relational assignment unless at least one candidate key will remain constant during an update and unless the database implicitly knows which one.

"Anith Sen" <anith_at_bizdatasolutions.com> wrote in message news:dtvco6$12a$1_at_emma.aioe.org...
>>> With those propositions, you can't, of course. Declaring name as the key
>>> is declaring that two people with the same name *are* the same person.
>>> Or perhaps more accurately, a table with person-names as the key is a
>>> table of names, not a table of people. Since names can't have a marital
>>> status, trying to map the table's attributes back to the real world
>>> breaks down.
>
> Agree. Regardless of being a surrogate or not, keys provide logical
> identity and it makes little sense to talk about any kind of constraints
> without them.
>
> --
> Anith
>
Received on Tue Feb 28 2006 - 06:43:12 CET