Re: Multiple-Attribute Keys and 1NF
Date: Thu, 30 Aug 2007 09:44:55 -0300
Message-ID: <46d6bb7b$0$4067$9a566e8b_at_news.aliant.net>
JOG wrote:
> On Aug 30, 1:42 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>JOG wrote:
>>
>>>>Write a predicate for the relation schema that when extentially quantified
>>>>and extended yields a set of atomic formulae that implies all three of the
>>>>propositions above. I think you'll find that the colour-code concept is in
>>>>that predicate.
>>
>>>I agree. I hold little stock with set based values so in RM I would go
>>>for the addition of colour-code foreign key.
>>
>>>But what if we weren't tied to a traditional relational schema and
>>>tweaked the system so it could allow propositions with more than one
>>>role of the same name without decomposing them. As Jan pointed out
>>>'tuples' are no longer functions - they would be unrestricted binary
>>>relations (subsets of attribute x values). We could produce a
>>>comparatively simpler and less cluttered schema, predicate in a very
>>>similar manner as before, and with a few simple alterations could have
>>>an equally effective WHERE mechanism. My concern however would be the
>>>consequences to JOIN.
>>
>>What would you offer in place of the RM's logical identity.
> > > Nothing. I am utterly convinced by Date et al's arguments in favour of > logical identity. (Why would I need to replace it?) I just wanna model > propositions, and they are always identified by their contents. >
In: {{(Color: green), (Color: yellow), (Type: earth)}}
What provides logical identity? Received on Thu Aug 30 2007 - 14:44:55 CEST