Re: weak entity
Date: Thu, 17 Oct 2002 21:29:55 +0100
Message-ID: <GWlgOYaD3xr9EwkW_at_diamond9.demon.co.uk>
In message <gcFp9.923$US2.10606_at_vixen.cso.uiuc.edu>, Ashutosh Galande
<galande_at_uiuc.edu> writes
>I totally agree with you. But what I don't understamd is, if adding external
>ID attribute to inherent attributes of an entity doesn't make it strong
>entity then we are fraught with a number of weak entities in real life. I
>have seen it to be a common practice to use ID attribute for entities. These
>attributes, as you noted are generated with additional processing outside
>the database. But still the ER diagram represents these entities as a strong
>entity. So why this anomaly?
The diagram is wrong, or at least misleading. What it should really show is the same weak entity plus a new strong entity with one attribute, the ID. There should be a 1:1 relationship between the new entity and the weak entity.
I think it's probably better to represent entities like this because it should remind system designers that the 1:1 relationship has to be maintained.
-- Bernard Peek bap_at_shrdlu.com www.diversebooks.com: SF & Computing book reviews and more..... In search of cognoscenti -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =-----Received on Thu Oct 17 2002 - 22:29:55 CEST