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An unfortunate side-effect

From: Francis McCabe <frankmccabe@mac.com>
Date: Thu, 9 Mar 2006 11:18:53 -0800
Message-Id: <A9C21A5D-66DD-481E-95EF-D790F1C59156@mac.com>
To: public-rif-wg@w3.org

I believe that it was Michael Kifer who noted:

> The implication of this is that RIF will have two completely disjoint
> things: declarative rules and production rules, and that we should  
> probably
> split into two subgroups.

I think that this misses the true import of my original comment.

1. My *real* issue was with the split between phase I and II;  
particular wrt the way that PRs were going to be handled.

2. If you believe that the kinds of issues with mapping are  
restricted between the extremes of PRs and predicate logic, then I am  
afraid you are in for a disappointment. It seems to me that there is  
at least as much potential for difficulty between different flavors  
of logic as between logic and PRs. E.g., all the different kinds of  
approximate reasoning, reasoning over sets of theories, DL versus LP,  
not to mention all the negative kinds of reasoning :)

3. I believe that there is a way of making progress that does not  
involve YARL (yet another rule language). This is in the area of  
marking up rule sets in a standardized way without trying to  
standardize the rule languages themselves.

As a straw man (YASM) one could imagine something like:

<ruleset language="prolog" variant="ISO" topic="ancestor">
   ancestor(X,Y) :- parent(X,Y).
   ancestor(X,Z) :- parent(X,Y), ancestor(Y,Z).
</ruleset>

This would allow meta-tools to process rulesets and decide for  
themselves whether to handle a given ruleset without trying to  
actually parse the ruleset first. I think that this could be quite  
useful in many cases of ruleset integration, but would not address  
the semantic interoperability issues.

One might choose to go on to have a standard abstract syntax, with an  
associated XML concrete syntax, that any rule language could be  
mapped to:

<ruleset language="prolog" variant="ISO" topic="ancestor"  
representation="RIF-XML">
   <rule>
     <head>
       <predication>
         <predicate name="ancestor"/>
          etc. etc.
</ruleset>

This would have the (perhaps marginal) benefit of allowing  
standardized processing of the syntax of different rule languages.

Note that there is not necessarily much implied semantics in this. No  
discussion about negation etc.

A third level of defining a meta-notation for semantics, so that we  
could construct the appropriate interpretation for a ruleset might  
look like:

<ruleset language="prolog" ...>
   <rof>
     <elimination="resolution"/>
     <negation="clark"/>
   </rof>
   <rule>
      ...
</ruleset>

This last phase, of course, would be the hardest to do. And perhaps  
have the least payback given any given rule engine is going to have a  
restricted pre-determined set of rules of inference that it 'knows'  
about.

Frank
Received on Thursday, 9 March 2006 19:19:04 GMT

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