[jboss-jira] [JBoss JIRA] (DROOLS-1001) Tabled Logic Programming-like mechanism to avoid infinite query recursion

[Fabian Meyer (JIRA)]

Fabian Meyer created DROOLS-1001:
------------------------------------

             Summary: Tabled Logic Programming-like mechanism to avoid infinite query recursion
                 Key: DROOLS-1001
                 URL: https://issues.jboss.org/browse/DROOLS-1001
             Project: Drools
          Issue Type: Feature Request
            Reporter: Fabian Meyer
            Assignee: Mark Proctor
            Priority: Optional


Queries, such as a transitive closure, will lead to an infinite query recursion in PHREAK:

{code:drl}
declare Resource 
	name : String @key
end

declare partOf
	subject : Resource @key
	object : Resource @key
end

rule "init"
	when
	then
	Resource a = new Resource("a");
	Resource b = new Resource("b");
	Resource c = new Resource("c");
	
	insert (new partOf(a,b));
	insert (new partOf(a,c));
end	

rule "print container"
	when
		trans_partOf(part, container;)
	then
		System.out.println(part + " partOf " + container);
end

query trans_partOf(Resource part, Resource container) 
	// Find direct asserted fact
	partOf(part,container;)
	or
	// Find the transitive closure
	trans_partOf(part, p;)
	and
	trans_partOf(p, container;)
end
{code}

The algorithm can easily be rewritten as a production rule, resulting in a huge amount of materialized facts in large knowledge bases, which are probably never needed. 

In Logic Programming,  a mechanism called Tabled Logic Programming is used to avoid such infinite recursion. Maybe the tabling mechanism can be adapted to PHREAK, in order to avoid fact materilization when using production rules instead of queries.



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