Re: deductive databases

From: alex goldman <hello_at_spamm.er>
Date: Sat, 14 May 2005 07:27:07 -0700
Message-Id: <1436952.HqgieSMmFo@yahoo.com>

VC wrote:

>
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:xVQge.89347$4x.5404810_at_phobos.telenet-ops.be...

>> alex goldman wrote:
>>> While people who responded seem to disagree on whether SQL has
>>> recursion,
>>
>> ?? I didn't see any disagreement. What the different answers told you was
>> that this differs per SQL standard and per implementation.
>>
>>> what about functors?
>>>
>>> For example, can you express something like this with SQL?
>>>
>>> for_any X Y : car(cons(X, Y), X)
>>
>> That depends on what you mean by "can express". Since SQL is a query
>> language in which you formulate queries over tables it can only formulate
>> queries over tables and not over functors. So in that sense the answer is
>> "no" but that observation is about as interesting as the fact that SQL
>> also cannot make coffee. If you reformulate it as a statement about
>> tables by, for example, modeling car as a binary table and cons as a
>> ternary table then you *can* express this and for that you don't even
>> need recursion.
>>
>> -- Jan Hidders

>
> It actually depends on what <alex goldman> means by
>
> a. 'Functor', the word that has different meaning in different
> PLs/contexts
>
> b. car(cons(X,Y), X). If it's Lisp, the expression does not make sense.
> If it's a Prolog 'functor', it does not make any sense either.

In the future, please add qualifiers like "to me" to silly statements like the above. Car of a cons, consisting of X and Y, is X. Received on Sat May 14 2005 - 09:27:07 CDT