Re: Use an alternative implementation of a FRuleEngineI

[Dave Reynolds]

On 15/04/14 14:55, Sébastien Boulet wrote:
Hi all,
i would like to use an alternative implementation of the FRuleEngineI. My 
problem is that the FRuleEngineI is instantiated directly from two locations :
in com.hp.hpl.jena.reasoner.rulesys.FBRuleInfGraph
     @Override
     protected void instantiateRuleEngine(List<Rule> rules) {
         if (rules != null) {
             if (useRETE) {
                 engine = new RETEEngine(this, rules);
             } else {
                 engine = new FRuleEngine(this, rules);
             }
         } else {
             if (useRETE) {
                 engine = new RETEEngine(this);
             } else {
                 engine = new FRuleEngine(this);
             }
         }
     }
and in com.hp.hpl.jena.reasoner.rulesys.RETERuleInfGraph

     @Override
     protected void instantiateRuleEngine(List<Rule> rules) {
         if (rules != null) {
             engine = new RETEEngine(this, rules);
         } else {
             engine = new RETEEngine(this);
         }
     }

For now, if i want to use another FRuleEngineI, i have to sub class theses 
classes for instantiating my own FRuleEngineI implementation. And since theses 
classes (FBRuleInfGraph, RETERuleInfGraph) are instantiated directly by others 
ones (GenericRuleReasoner, FBRuleReasoner, OWLFBRuleReasoner…), i will have to 
sub class a lot of existing classes.

So my question is, is there an easiest way to do this ?

No. It's not be a usecase that's come up before. People have sometimes 
done custom versions of FBRuleInfGraph or created new sorts of InfGraph 
but I'm not aware of anyone previously replacing the forward engine 
across all existing InfGraph types.

If not, i was thinking of introducing a singleton FRuleEngineIFactory (I kept 
the useRETE  flag for backward compatibility.) :

[Yeah the non-RETE engine and the useRETE flag ought to be removed 
sometime but for now it's in there.]

public class FRuleEngineIFactory {
     private static FRuleEngineIFactory instance;

[needs to be initialized :)]

     public static void setInstance(FRuleEngineIFactory instance) { 
FRuleEngineIFactory.instance = instance; }
     public FRuleEngineIFactory getInstance() { return instance; }

     public FRuleEngineI createFRuleEngineI(ForwardRuleInfGraphI parent, 
List<Rule> rules, boolean useRETE) {
         FRuleEngineI engine;
         if (rules != null) {
             if (useRETE) {
                 engine = new RETEEngine(parent, rules);
             } else {
                 engine = new FRuleEngine(parent, rules);
             }
         } else {
             if (useRETE) {
                 engine = new RETEEngine(parent);
             } else {
                 engine = new FRuleEngine(parent);
             }
         }
         return engine;
     }
}

This factory might be used by

com.hp.hpl.jena.reasoner.rulesys.FBRuleInfGraph
     @Override
     protected void instantiateRuleEngine(List<Rule> rules) {
         engine = FRuleEngineIFactory.getInstance().createFRuleEngineI(this, 
rules, useRETE);
     }

and by com.hp.hpl.jena.reasoner.rulesys.RETERuleInfGraph
     @Override
     protected void instantiateRuleEngine(List<Rule> rules) {
         engine = FRuleEngineIFactory.getInstance().createFRuleEngineI(this, 
rules, true);
     }

And i could replace the factory instance by my own instance :

         FRuleEngineIFactory.setInstance(new CustomFRuleEngineIFactory());


What do you think of that ?

Sure. That would enable the sort of plug point you are after without 
causing knock on problems.

Dave