Re: compound propositions

From: Bob Badour <>
Date: Thu, 18 Mar 2010 14:09:05 -0300
Message-ID: <4ba25dbd$0$12465$>

paul c wrote:

> David BL wrote:
> ...

>> So back to your statement, I would say that there is a 1:1
>> correspondence from relation (= set of tuples) to a boolean valued
>> function that is true for tuples in that relation and false
>> otherwise.

Indeed. One is the predicate and the other is the extension of the predicate. A relation is an extension of a predicate.

>> This boolean valued function can be said to represent a
>> predicate under an interpretation but I'm not sure if that's what you
>> mean.  More specifically, what do you mean by "satisfy" when you say
>> relations satisfy predicates?
>> ...

> A relation satisfies one or more predicates when its attribute names

How do you figure "or more" ?

> match the variable names apparent in the predicates and the attribute
> types are applicable for whatever manipulations (eg., aggregation) the
> predicate states.

In other words, the extension of a predicate is the set of all tuples that satisfy the predicate.

> (I just say 'satisfies' to avoid suggesting that a predicate has a truth
> value. Don't see anything wrong with talking about correspondence
> between relations and functions, just seems more to the point to think
> of another correspondence - tuples that indicate whether propositions
> are true or false.)
Received on Thu Mar 18 2010 - 18:09:05 CET

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