Re: Lucid statement of the MV vs RM position?

From: paul c <toledobythesea_at_oohay.ac>
Date: Tue, 02 May 2006 16:37:25 GMT
Message-ID: <9VL5g.106714$WI1.4693@pd7tw2no>

Jon Heggland wrote:
> David Cressey wrote:
>

>>In Ted Codd's 1970 paper,  he points out that when a system of relations is
>>devised to store a body of facts,  there are other systems of relations that
>>will express precisely the same body of facts.  He then points out that
>>within a group of such systems that are all logically equivalent,  there
>>will be (at least) one that contains no sets, lists, or RVAs as elements of
>>a tuple.

>
>
> ....on two conditions:
>
> "(1) The graph of interrelationships of the nonsimple
> domains is a collection of trees.
> (2) No primary key has a component domain which is
> nonsimple.
> The writer knows of no application which would require
> any relaxation of these conditions."
>
> Other writers claim they *do* know of such applications, however, and
> have proposed (semi-)formal guidelines for identifying cases where RVAs
> may be appropriate.
> ...

An example that some may not find very interesting, ie., too simple but still troubles me might be "the sets/combinations of parts that a supplier will agree to ship" having no other attributes than S# and P#, eg., SP { S#, {P#}} where I'm intending {P#} to mean a set of parts. I'm interested to know of the other writers or what they say.

pc Received on Tue May 02 2006 - 11:37:25 CDT