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Re: Identifying Relation vs Non-Identifying?

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Fri, 01 Jul 2005 23:27:48 GMT
Message-ID: <Ujkxe.135103$ej.7213120@phobos.telenet-ops.be>


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.

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".

Hope that helps,

Received on Fri Jul 01 2005 - 18:27:48 CDT

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