Re: Identifying Relation vs Non-Identifying?
Date: Tue, 05 Jul 2005 10:57:14 -0500
Message-ID: <v5yye.5$JM6.552_at_news.uswest.net>
On 7/1/2005 6:27 PM, Jan Hidders wrote:
> Dan wrote:
>
>> >> Can someone explain to be me the difference to between an identifying >> relation and a non-identifying relation? I came across these terms >> when I recently started looking into using ERM tool.
>
>
> Don't you mean an "identifying relation*ship*"? Be careful not to
> confuse the notions of relationship as used in ERDs and relation as used
> in the Relational Model.
>
The 2 tools call it a "relation". Since it is for drawing a line between tables (relations), I guess they should call it "relationship".
> Loosely speaking an identifying relationship is a relationship that is
> necessary to identify a certain entity that plays a role in it. Consider
> for example the relationship "owns" between "Person" and "Dog" where
> "Dog" only has attribute "name". In that case a dog is probably not
> uniquely identified by just its name, but it will be by a combination of
> name and owner. In some sense you could say that the relationship "owns"
> is part of the key of "Dog". And that makes it an identifying
> relationship. Also google for "weak entity".
Makes sense to me.
> Hope that helps,
>
> -- Jan Hidders
Thanks Jan.
Dan Received on Tue Jul 05 2005 - 17:57:14 CEST