Re: Multiple-Attribute Keys and 1NF
Date: Thu, 30 Aug 2007 13:00:53 -0300
Message-ID: <46d6e969$0$4065$9a566e8b_at_news.aliant.net>
JOG wrote:
> On Aug 30, 2:55 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>JOG wrote:
>>
>>>On Aug 30, 1:44 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>>
>>>>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?
>>
>>>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?
>>
>>I haven't got a clue what you said.
> > > I just regurgitated leibniz identity. > >
>>In the RM, every value is uniquely
>>identifiable by the combination of relation name, attribute name and any
>>candidate key value. That's logical identity as it was originally
>>spelled out.
>>
>>Two values above have the same attribute name.
> > Now you've lost me. A "value" is not identifiable by its relation name > and attribute name. This makes no sense to me. Where in predicate > logic does that come from? A value is just a value. It is identifiable > in its own right as being an individual from a domain.
I mispoke. "Any value represented in a relvar"
> An individual piece of /data/ however (which is perhaps what you mean > by a value) has an identity made up of a combination of an attribute > name and a corresponding value. One needs both to identify the data > item. A proposition in turn is identifiable by its contents, which is > a set of those data items. Regards, J.
I repeat: two pieces of data have the same name, Color. Received on Thu Aug 30 2007 - 18:00:53 CEST