Re: deductive databases

"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

1. 'Functor', the word that has different meaning in different PLs/contexts
2. 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.