Re: [RIF] A Modest Proposal: Work Out Some Concrete Examples; Example-1: CHANGE-BABY-IF-WET rule

Peter F. Patel-Schneider" <pfps@inf.unibz.it> writes:
>
> > Francois Bry <bry@ifi.lmu.de> wrote:
> > >
> > > I agree that RIF should have (1) a clear declarative semantics and (2) 
> > > in addition support conveying *some* *limited* specifications of 
> > > procedural semantics (eg backward chaining is intended because with 
> > > forward chaining the considered rules would require to process all/too 
> > > many nodes on the Web).
> > 
> > I disagree with that, especially with the statement that "with forward
> > chaining the considered rules would require to process all/too many nodes
> > on the Web".
> 
> +[some very large number]
> 
> What makes "forward chaining" a particularly bad method, even if you think of
> forward chaining as a way to perform saturation?  Forward chaining (including
> saturation, or not) works exceedingly well in some situations (and exceedingly
> poorly in others).  Standard backward chaining has exactly the same
> characteristics, by the way.  It all depends on the situation, and the
> parameters used to control the chaining.

There are well-known techniques to control bottom-up evaluation, which
makes it not worse than top-down (at least in theory).

> > This is all a matter for the query optimizer to resolve.
> 
> Well, it is all a matter for some piece of softare to resolve.  This may
> or may not be something like a "query optimizer".

Well, I was using the terminology of databases because this issue of
top-down vs. bottom-up has been rehashed many times in that community.  I
thought that the issue of which one (t-d or b-u) is better has been laid to
rest a decade ago.


	--michael

Received on Wednesday, 1 February 2006 20:57:59 UTC