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Re: Smart Database Tricks

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 22 Jun 2007 10:35:03 -0300
Message-ID: <467bcffb$0$4305$9a566e8b@news.aliant.net>


Jan Hidders wrote:
> On 22 jun, 14:25, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>

>>Jan Hidders wrote:
>>
>>>On 22 jun, 01:36, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>>
>>>>Jan Hidders wrote:
>>
>>>>>On 21 jun, 21:17, vldm10 <vld..._at_yahoo.com> wrote:
>>
>>>>>>On Jun 18, 7:41 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
>>
>>>>>>>On 18 jun, 20:59, vldm10 <vld..._at_yahoo.com> wrote:
>>
>>>>[snip]
>>
>>>>>>>If this is a relation then
>>>>>>>all columns are attributes and since you have represented all the
>>
>>>>>>Can you please, tell me what is the definition of the attribute in RM.
>>
>>>>>It's a column of a relation. Conceptually it represent the role in the
>>>>>predicate that is represented by the relation.
>>
>>>>Is an attribute a predicate variable of some sort?
>>
>>>As in "the x in predicate P(x, y) "? Yes, I'd say that is the same
>>>thing.
>>
>>I thought so. When one writes a query and requests certain attributes,
>>would those requested attributes be free variables in a logic sense?

>
>
> That's not how I would formulate it. Strictly speaking the attribute
> is a position or role in a predicate. So if the predicate is P(x, y)
> then there are two positions / attributes: the first position where x
> is bound and the second position where y is bound. It doesn't really
> make sense to say that the variable is the attribute because how then
> would you describe the situation in the formula "P(x, y) and Q(x, x)"?
> Is the variable 'x' an attribute? It makes more sense to say that it
> is a variable that is bound to the first position / attribute of P and
> the first and second posiiton / attribute of Q.
>
> So, er, I guess my previous answer should actually have been "no, not
> exactly". ;-)

Thank you, that clarifies things for me. Received on Fri Jun 22 2007 - 08:35:03 CDT

Original text of this message

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