Re: Does entity integrity imply entity identity?
Date: Sat, 01 Aug 2009 21:54:17 GMT
"David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message
> "Mr. Scott" <do_not_reply_at_noone.com> wrote in message
>> Since the entity integrity rule ensures that a relational table cannot
>> have any duplicate rows, does that imply that each row in a table maps to
>> a distinct entity?
> It's more reasonable to say that a tuple can be understood to represent
> some fact which is normally assumed to be true. Entity = Thing. I don't
> see any special reason why a tuple MUST map to a "thing" (whatever that
> means) but if you find that interpretation useful then use it.
> The concept of "Entity Integrity" is not much more than a restatement of
> what a relation is anyway.
It is useful to think of some tables as representing the attributes of subject matter entities. In this context, the entity integrity rule just says that every instance of an entity can be identified by its key data.
Some peopl, especially the regulars in c.d.t. don't use the concept of subject matter entities in their discussion of relational data. So be it. Received on Sat Aug 01 2009 - 23:54:17 CEST