/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hp.hpl.jena.reasoner.rulesys.impl;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.hp.hpl.jena.graph.Triple;
import com.hp.hpl.jena.reasoner.ReasonerException;
import com.hp.hpl.jena.reasoner.TriplePattern;
import com.hp.hpl.jena.reasoner.rulesys.BindingEnvironment;
import com.hp.hpl.jena.reasoner.rulesys.Builtin;
import com.hp.hpl.jena.reasoner.rulesys.ForwardRuleInfGraphI;
import com.hp.hpl.jena.reasoner.rulesys.Functor;
import com.hp.hpl.jena.reasoner.rulesys.Rule;
import com.hp.hpl.jena.reasoner.rulesys.RuleDerivation;
/**
* Manages a set of ready-to-fire rules. For monotonic rule sets
* we simply fire the rules as soon as they are triggered. For non-monotonic
* rule sets we stack them up in a conflict set and fire them one-at-a-time,
* propagating all changes between times.
* <p>
* Note, implementation is not thread-safe. Would be easy to make it so but
* concurrent adds to InfModel are not supported anyway.
*
* @author <a href="mailto:der@hplb.hpl.hp.com">Dave Reynolds</a>
* @version $Revision: 1.2 $
*/
public class RETEConflictSet {
protected static Logger logger = LoggerFactory.getLogger(FRuleEngine.class);
/** the execution context for this conflict set */
protected RETERuleContext gcontext;
/** false if the overall rule system contains some non-montotonic rules */
protected boolean isMonotonic;
/** the list of rule activations left to fire */
protected ArrayList<CSEntry> conflictSet = new ArrayList<CSEntry>();
/** count the number of positive entries - optimization hack */
protected int nPos = 0;
/** count the number of negative entries - optimization hack */
protected int nNeg = 0;
/** Construct an empty conflict set, noting whether the overall rule system is monotonic or not */
public RETEConflictSet(RETERuleContext context, boolean isMonotonic) {
this.gcontext = context;
this.isMonotonic = isMonotonic;
}
/**
* Record a request for a rule firing. For monotonic rulesets it may be
* actioned immediately, otherwise it will be stacked up.
*/
public void add(Rule rule, BindingEnvironment env, boolean isAdd) {
if (isMonotonic) {
RETERuleContext context = new RETERuleContext((ForwardRuleInfGraphI)gcontext.getGraph(), gcontext.getEngine());
context.setEnv(env);
context.setRule(rule);
execute(context, isAdd);
} else {
// Add to the conflict set, compressing +/- pairs
boolean done = false;
if ( (isAdd && nNeg > 0) || (!isAdd && nPos > 0) ) {
for (Iterator<CSEntry> i = conflictSet.iterator(); i.hasNext(); ) {
CSEntry cse = i.next();
if (cse.rule != rule) continue;
if (cse.env.equals(env)) {
if (isAdd != cse.isAdd) {
i.remove();
if (cse.isAdd) nPos--; else nNeg --;
done = true;
} else {
// Redundant insert? Probably leave in for side-effect cases like print
}
}
}
}
if (!done) {
conflictSet.add(new CSEntry(rule, env, isAdd));
if (isAdd) nPos++; else nNeg++;
}
}
}
/**
* Return true if there are no more rules awaiting firing.
*/
public boolean isEmpty() {
return conflictSet.isEmpty();
}
/**
* Pick on pending rule from the conflict set and fire it.
* Return true if there was a rule to fire.
*/
public boolean fireOne() {
if (isEmpty()) return false;
int index = conflictSet.size() - 1;
CSEntry cse = conflictSet.remove(index);
if (cse.isAdd) nPos--; else nNeg --;
RETERuleContext context = new RETERuleContext((ForwardRuleInfGraphI)gcontext.getGraph(), gcontext.getEngine());
context.setEnv(cse.env);
context.setRule(cse.rule);
if (context.shouldStillFire()) {
execute(context, cse.isAdd);
}
return true;
}
/**
* Execute a single rule firing.
*/
public static void execute(RETERuleContext context, boolean isAdd) {
Rule rule = context.getRule();
BindingEnvironment env = context.getEnv();
ForwardRuleInfGraphI infGraph = (ForwardRuleInfGraphI)context.getGraph();
if (infGraph.shouldTrace()) {
logger.info("Fired rule: " + rule.toShortString());
}
RETEEngine engine = context.getEngine();
engine.incRuleCount();
List<Triple> matchList = null;
if (infGraph.shouldLogDerivations() && isAdd) {
// Create derivation record
matchList = new ArrayList<Triple>(rule.bodyLength());
for (int i = 0; i < rule.bodyLength(); i++) {
Object clause = rule.getBodyElement(i);
if (clause instanceof TriplePattern) {
matchList.add(env.instantiate((TriplePattern)clause));
}
}
}
for (int i = 0; i < rule.headLength(); i++) {
Object hClause = rule.getHeadElement(i);
if (hClause instanceof TriplePattern) {
Triple t = env.instantiate((TriplePattern) hClause);
// Used to filter out triples with literal subjects
// but this is not necessary
// if (!t.getSubject().isLiteral()) {
// Only add the result if it is legal at the RDF level.
// E.g. RDFS rules can create assertions about literals
// that we can't record in RDF
if (isAdd) {
if ( ! context.contains(t) ) {
engine.addTriple(t, true);
if (infGraph.shouldLogDerivations()) {
infGraph.logDerivation(t, new RuleDerivation(rule, t, matchList, infGraph));
}
}
} else {
if ( context.contains(t)) {
// Remove the generated triple
engine.deleteTriple(t, true);
}
}
// }
} else if (hClause instanceof Functor && isAdd) {
Functor f = (Functor)hClause;
Builtin imp = f.getImplementor();
if (imp != null) {
imp.headAction(f.getBoundArgs(env), f.getArgLength(), context);
} else {
throw new ReasonerException("Invoking undefined Functor " + f.getName() +" in " + rule.toShortString());
}
} else if (hClause instanceof Rule) {
Rule r = (Rule)hClause;
if (r.isBackward()) {
if (isAdd) {
infGraph.addBRule(r.instantiate(env));
} else {
infGraph.deleteBRule(r.instantiate(env));
}
} else {
throw new ReasonerException("Found non-backward subrule : " + r);
}
}
}
}
// Inner class representing a conflict set entry
private static class CSEntry {
protected Rule rule;
protected BindingEnvironment env;
protected boolean isAdd;
CSEntry(Rule rule, BindingEnvironment env, boolean isAdd) {
this.rule = rule;
this.env = env;
this.isAdd = isAdd;
}
}
}