Re: Multiple-Attribute Keys and 1NF

Date: Thu, 30 Aug 2007 10:55:02 -0300
Message-ID: <46d6cbea\$0\$4024\$9a566e8b_at_news.aliant.net>

```>>JOG 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?
```

>
> I may be misunderstanding you, but let me take a stab. The identity of
> any set of course lies in its elements (i.e. in this of a single
> propositions, the ordered pairs). Given we know Colors are the
> antecedents in the proposition we are modelling, this has to be been
> defined in the collectivizing predicate for the whole collection of
> rows. We also know therefore there may not exist another set of pairs
> containing the same Colors, so we can identify the whole proposition
> through examination of just those roles. All works just as per normal
> in RM. Is this what you meant?

Two values above have the same attribute name. Received on Thu Aug 30 2007 - 15:55:02 CEST

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