# Re: compound propositions

From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 18 Mar 2010 21:21:16 GMT
Message-ID: <gPwon.68458\$Db2.38232_at_edtnps83>

> paul c wrote:
>

```>> Bob Badour wrote:
>>
>>> paul c 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.
> ...

I didn't give a formal definition and didn't pretend to (my disclaimer was snipped). Received on Thu Mar 18 2010 - 22:21:16 CET

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