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Re: predicate, constraints, header, relvar, and relation

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 21 Apr 2007 22:23:51 GMT
Message-ID: <X9wWh.26809$PV3.275974@ursa-nb00s0.nbnet.nb.ca>


davis.jeffrey_at_gmail.com wrote:

> On Apr 20, 5:26 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>

>>Both. The data types of the attributes are part of the predicates of
>>both the variable and the value. Generally speaking, the most specific
>>type of any attribute of the value will be a subtype of the declared
>>type of the variable.

>
> Thanks. This makes it much more clear.

Strictly speaking, it is incorrect to speak of a value having a predicate. A value is or is part of a proposition used to instantiate a predicate. See http://www.earlham.edu/~peters/courses/log/terms3.htm

Data types etc. are properties of values, and predicates identify required properties. In a sense, a relvar is a named predicate.

I apologize for misspeaking earlier.

>>It certainly makes sense to draw attention to the important properties
>>of a literal in a given context. I could see someone wanting to overload
>>the constraint concept to achieve this goal, but I think that would be a
>>mistake.

>
> Ok, I see.
>
> Thanks for the insightful reply!
Received on Sat Apr 21 2007 - 17:23:51 CDT

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