Re: compound propositions

From: Bob Badour <>
Date: Thu, 18 Mar 2010 18:14:43 -0300
Message-ID: <4ba2974e$0$12423$>

paul c wrote:

> Bob Badour wrote:

>> paul c wrote:
>>> Bob Badour wrote:
>>>> paul c wrote:
>>>>> David BL wrote:
>>>>> ...
>>>>>> 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?
>>>>>> ...
>>> ...
>>>>> 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.
>>>> ...
>>> Yes, but David B asked what 'satisfy' means.
>> In that case, I suggest you not shy away from equality and boolean 
>> truth values. Unless you can think of a situation where "satisfy" 
>> means something other than "predicate evaluates to true".

> I don't know why the fuss about the word 'satisfy'! Admittedly its
> casual but some big names use it from time to time. I certainly wasn't
> trying to alter anybody's vocabulary but I like it because it encourages
> me to distinguish header from value which helps me think concretely
> about implementation. I just don't see the usefulness of repetitious
> acknowledgement that 'it is always true that there is a set of
> featherless bipeds'.

I, too, find your use of the word sloppy, because a relation is a set of things that satisfy a predicate. The relation, itself, doesn't satisfy the predicate. Extent or extension is well-defined as a set of instances and describes what a relation is: a set of instances that satisfy a predicate.

I am not suggesting you never use the word "satisfy". I'm merely suggesting more careful use and a different approach when asked for a definition.

Sloppy thinking doesn't lead to profound insight--it leads to an illusion of insight and to an illusion of profundity. To think outside the box, one must first be able to describe the box with great precision. Received on Thu Mar 18 2010 - 22:14:43 CET

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