8:48 p.m.
You will have to use regular insert() instead of insertLogical(). This is
because:
rule "reachDirect"
salience 10
when
e : Edge(s1 : source, t1 : target)
not( Reach(source == s1, target == t1) )
then
insertLogical( new Reach(e.getSource(),e.getTarget()) );
System.out.println( "Reach " + e.getSource() + "," +
e.getTarget() );
end
Is initially true, but once the consequence is executed, the insert(new
Reach()) will cause the pattern "not(Reach(...))" to become false and so the
object is retracted, causing the recursion.
[]s
Edson
2008/7/3, Paul Fodor <paul.i.fodor(a)gmail.com>:
On Thu, Jul 3, 2008 at 3:56 PM, Paul Fodor <paul.i.fodor(a)gmail.com> wrote:
> Dear Sir,
>
> I am new to Drools and I want to ask how can I implement the classical
> transitive closure in Drools. For instance we have a bunch of facts
> edge/2 and the transitive closure:
>
> reach(X,Y):- edge(X,Y).
> reach(X,Y):- edge(X,Z),reach(Z,Y).
My current version looks like the following, but it never terminates.
It re-derives reach(c,c) forever.
TransitiveClosure.drl :
package org.drools.examples
import org.drools.examples.TransitiveClosureExample.Edge;
import org.drools.examples.TransitiveClosureExample.Reach;
rule "reachDirect"
salience 10
when
e : Edge(s1 : source, t1 : target)
not( Reach(source == s1, target == t1) )
then
insertLogical( new Reach(e.getSource(),e.getTarget()) );
System.out.println( "Reach " + e.getSource() + "," +
e.getTarget()
);
end
rule "reachIndirect"
salience 10
when
e : Edge(s1 : source, t1 : target)
r : Reach(t2 : target, source == t1 )
not( Reach(source == s1, target == t2) )
then
insertLogical( new Reach(e.getSource(),r.getTarget()) );
System.out.println( "Reach " + e.getSource() + "," +
r.getTarget()
);
end
TransitiveClosureExample.java :
package org.drools.examples;
import java.io.InputStreamReader;
import org.drools.RuleBase;
import org.drools.RuleBaseFactory;
import org.drools.StatefulSession;
import org.drools.audit.WorkingMemoryFileLogger;
import org.drools.compiler.PackageBuilder;
import org.drools.compiler.PackageBuilderConfiguration;
public class TransitiveClosureExample {
public static void main(final String[] args) throws Exception {
PackageBuilderConfiguration conf = new
PackageBuilderConfiguration();
final PackageBuilder builder = new PackageBuilder( conf );
builder.addPackageFromDrl( new InputStreamReader(
TransitiveClosureExample.class.getResourceAsStream(
"TransitiveClosure.drl" ) ) );
final RuleBase ruleBase = RuleBaseFactory.newRuleBase();
ruleBase.addPackage( builder.getPackage() );
final StatefulSession session = ruleBase.newStatefulSession();
final WorkingMemoryFileLogger logger = new
WorkingMemoryFileLogger( session );
logger.setFileName( "log/transitiveClosure" );
final Edge edgeAB = new Edge( "a","b" );
final Edge edgeBC = new Edge( "b","c" );
final Edge edgeCD = new Edge( "c","d" );
session.insert( edgeAB );
session.insert( edgeBC );
session.insert( edgeCD );
session.fireAllRules();
logger.writeToDisk();
session.dispose();
}
public static class Edge {
private String source;
private String target;
public Edge() {}
public Edge(String source, String target) {
super();
this.source = source;
this.target = target;
}
public String getSource() {
return source;
}
public String getTarget() {
return source;
}
}
public static class Reach {
private String source;
private String target;
public Reach() {}
public Reach(String source, String target) {
super();
this.source = source;
this.target = target;
}
public void setSource(String source) {
this.source = source;
}
public String getSource() {
return source;
}
public void setTarget(String target) {
this.target = target;
}
public String getTarget() {
return target;
}
}
}
Any sugestion?
Regards,
Paul Fodor
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Edson Tirelli
JBoss Drools Core Development
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