Re: Composite attributes
Date: Tue, 19 Nov 2002 05:28:28 GMT
Message-ID: <3DD9CBDA.4030106_at_earthlink.net>
Juan Pardillos wrote:
> I'd like to know if a composite attribute (e.g., a subject code like
> 'CS2323', where 'CS' denotes the department and so on) can be in a
> relation or whether this is prohibited by the definition of relation.
> In other words, does the definition of relation prohibit composite
> attributes or only multivalued attributes?.
As Larry Coon said, that isn't normally regarded as a composite attribute.
C J Date has weighed in arguing against keys such as that in "Don't Encode Information Into Primary Keys" - chapter 30 in "Relational Database Writings 1989-1991" - and there are related chapters 31 "Composite Keys" and 32 "Composite Foreign Keys and Nulls" too.
> I've got the same doubt regarding the first normal form. Depending on
> the text, I get a different opinion about the answer to this question.
This has been discussed recently in Database Debunkings - http://www.dbdebunk.com/ - and not in wholly vitriolic terms, either. Which books did you read to get different answers?
-- Jonathan Leffler #include <disclaimer.h> Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com Guardian of DBD::Informix 1.00.PC2 -- http://dbi.perl.org/Received on Tue Nov 19 2002 - 06:28:28 CET