Re: Identifying Relation vs Non-Identifying?

From: Dan <dan_at_nospam.com>
Date: Tue, 05 Jul 2005 10:57:14 -0500
Message-ID: <v5yye.5$JM6.552@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 - 10:57:14 CDT