| /* |
| * 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 org.apache.rya.forwardchain.rule; |
| |
| import java.util.Collection; |
| import java.util.HashSet; |
| import java.util.Map; |
| import java.util.Set; |
| import java.util.concurrent.ConcurrentHashMap; |
| |
| import org.apache.log4j.Logger; |
| import org.eclipse.rdf4j.query.algebra.StatementPattern; |
| |
| import com.google.common.base.Preconditions; |
| |
| /** |
| * Represents a set of forward-chaining {@link Rule}s and their relationships. |
| */ |
| public class Ruleset { |
| private final Set<Rule> rules; |
| private final Map<Rule, Set<Rule>> successors; |
| private final Map<Rule, Set<Rule>> predecessors; |
| |
| private final Logger logger = Logger.getLogger(this.getClass()); |
| |
| /** |
| * Constructor. Takes in a set of rules and determines their dependencies. |
| * @param rules The complete set of rules to process; should not be null. |
| */ |
| public Ruleset(Collection<Rule> rules) { |
| Preconditions.checkNotNull(rules); |
| this.rules = new HashSet<>(); |
| for (Rule rule : rules) { |
| if (rule != null) { |
| this.rules.add(rule); |
| } |
| } |
| successors = new ConcurrentHashMap<>(); |
| predecessors = new ConcurrentHashMap<>(); |
| // Build the dependency graph of all the rules, in both directions |
| for (Rule rule : rules) { |
| successors.put(rule, new HashSet<>()); |
| predecessors.put(rule, new HashSet<>()); |
| } |
| for (Rule rule1 : rules) { |
| for (Rule rule2 : rules) { |
| if (canTrigger(rule1, rule2)) { |
| logger.trace("\t" + rule1.toString() + " can trigger " + rule2.toString()); |
| successors.get(rule1).add(rule2); |
| predecessors.get(rule2).add(rule1); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Get the rules associated with this ruleset. |
| * @return The complete set of rules. |
| */ |
| public Set<Rule> getRules() { |
| return rules; |
| } |
| |
| /** |
| * Given a rule, return the set of all rules that it may trigger. That is, |
| * if the rule were to produce inferences, those inferences might directly |
| * cause other rules to apply in turn. |
| * @param precedingRule The potentially triggering rule; not null. |
| * @return All rules that could be triggered by the given rule. |
| */ |
| public Collection<Rule> getSuccessorsOf(Rule precedingRule) { |
| Preconditions.checkNotNull(precedingRule); |
| return successors.get(precedingRule); |
| } |
| |
| /** |
| * Given a rule, return the set of all rules that could trigger it. That is, |
| * if any one of those rules were applied, their potential conclusions could |
| * directly cause the specified rule to apply in turn. |
| * @param dependentRule The potentially triggered rule; not null. |
| * @return All rules that could trigger the given rule. |
| */ |
| public Collection<Rule> getPredecessorsOf(Rule dependentRule) { |
| Preconditions.checkNotNull(dependentRule); |
| return predecessors.get(dependentRule); |
| } |
| |
| /** |
| * Given a pair of rules, determine whether a path exists from the first to |
| * the second. That is, whether the first rule precedes the second rule |
| * either directly or transitively. If either rule is null, no path exists. |
| * @param r1 The start of the path |
| * @param r2 The end of the path |
| * @return whether a forward path exists. |
| */ |
| public boolean pathExists(Rule r1, Rule r2) { |
| if (r1 == null || r2 == null) { |
| return false; |
| } |
| Set<Rule> forwardFrontier = new HashSet<>(); |
| Set<Rule> backwardFrontier = new HashSet<>(); |
| Set<Rule> visitedForward = new HashSet<>(); |
| Set<Rule> visitedBackward = new HashSet<>(); |
| forwardFrontier.addAll(getSuccessorsOf(r1)); |
| backwardFrontier.add(r2); |
| while (!forwardFrontier.isEmpty() && !backwardFrontier.isEmpty()) { |
| Set<Rule> currentGoals = new HashSet<>(backwardFrontier); |
| for (Rule goal : currentGoals) { |
| if (forwardFrontier.contains(goal)) { |
| return true; |
| } |
| else { |
| visitedBackward.add(goal); |
| backwardFrontier.addAll(getPredecessorsOf(goal)); |
| } |
| } |
| backwardFrontier.removeAll(visitedBackward); |
| Set<Rule> currentSources = new HashSet<>(forwardFrontier); |
| for (Rule source : currentSources) { |
| if (backwardFrontier.contains(source)) { |
| return true; |
| } |
| else { |
| visitedForward.add(source); |
| forwardFrontier.addAll(getSuccessorsOf(source)); |
| } |
| } |
| forwardFrontier.removeAll(visitedForward); |
| } |
| return false; |
| } |
| |
| /** |
| * Whether the first rule can, in any circumstance, directly trigger the second. |
| * @param rule1 The first rule, which may produce some inferences |
| * @param rule2 The second rule, which may use the first rule's conclusions |
| * @return True if the first rule's conclusions could be used by the second. |
| */ |
| private boolean canTrigger(Rule rule1, Rule rule2) { |
| if (rule1 == null || rule2 == null) { |
| return false; |
| } |
| for (StatementPattern antecedent : rule2.getAntecedentPatterns()) { |
| if (rule1.canConclude(antecedent)) { |
| return true; |
| } |
| } |
| return false; |
| } |
| } |