/*
* 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.clerezza.rdf.utils;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.apache.clerezza.rdf.core.BNode;
import org.apache.clerezza.rdf.core.Graph;
import org.apache.clerezza.rdf.core.MGraph;
import org.apache.clerezza.rdf.core.NonLiteral;
import org.apache.clerezza.rdf.core.Resource;
import org.apache.clerezza.rdf.core.Triple;
import org.apache.clerezza.rdf.core.TripleCollection;
import org.apache.clerezza.rdf.core.impl.SimpleMGraph;
/**
* Utility methods to manipulate <code>MGraph</code>s
*
* @author reto
*/
public class MGraphUtils {
/**
* Removes a subGraph from an MGraph. The subGraph must match a subgraph of
* MGraph so that for every node in <code>subGraph</code>
* each triple it appears in is also present in <code>mGraph</code>. Two
* bnodes are considered equals if their contexts (as returned by
* <code>GraphNode.getNodeContext</code> are equals.
*
* @param mGraph
* @param subGraph
* @throws org.apache.clerezza.rdf.utils.MGraphUtils.NoSuchSubGraphException
*/
public static void removeSubGraph(MGraph mGraph, TripleCollection subGraph)
throws NoSuchSubGraphException {
//point to triples of mGraph that are to be removed (if something is removed)
final Set<Triple> removingTriples = new HashSet<Triple>();
//we first check only the grounded triples and put the non-grounded in here:
final TripleCollection unGroundedTriples = new SimpleMGraph();
for (Triple triple : subGraph) {
if (isGrounded(triple)) {
if (!mGraph.contains(triple)) {
throw new NoSuchSubGraphException();
}
removingTriples.add(triple);
} else {
unGroundedTriples.add(triple);
}
}
//we first remove the context of bnodes we find in object position
OBJ_BNODE_LOOP: while (true) {
final Triple triple = getTripleWithBNodeObject(unGroundedTriples);
if (triple == null) {
break;
}
final GraphNode objectGN = new GraphNode(triple.getObject(), unGroundedTriples);
NonLiteral subject = triple.getSubject();
Graph context = objectGN.getNodeContext();
Iterator<Triple> potentialIter = mGraph.filter(subject, triple.getPredicate(), null);
while (potentialIter.hasNext()) {
try {
final Triple potentialTriple = potentialIter.next();
BNode potentialMatch = (BNode)potentialTriple.getObject();
final Graph potentialContext = new GraphNode(potentialMatch, mGraph).getNodeContext();
if (potentialContext.equals(context)) {
removingTriples.addAll(potentialContext);
unGroundedTriples.removeAll(context);
continue OBJ_BNODE_LOOP;
}
} catch (ClassCastException e) {
continue;
}
}
throw new NoSuchSubGraphException();
}
SUBJ_BNODE_LOOP: while (true) {
final Triple triple = getTripleWithBNodeSubject(unGroundedTriples);
if (triple == null) {
break;
}
final GraphNode subjectGN = new GraphNode(triple.getSubject(), unGroundedTriples);
Resource object = triple.getObject();
if (object instanceof BNode) {
object = null;
}
Graph context = subjectGN.getNodeContext();
Iterator<Triple> potentialIter = mGraph.filter(null, triple.getPredicate(), object);
while (potentialIter.hasNext()) {
try {
final Triple potentialTriple = potentialIter.next();
BNode potentialMatch = (BNode)potentialTriple.getSubject();
final Graph potentialContext = new GraphNode(potentialMatch, mGraph).getNodeContext();
if (potentialContext.equals(context)) {
removingTriples.addAll(potentialContext);
unGroundedTriples.removeAll(context);
continue SUBJ_BNODE_LOOP;
}
} catch (ClassCastException e) {
continue;
}
}
throw new NoSuchSubGraphException();
}
mGraph.removeAll(removingTriples);
}
private static boolean isGrounded(Triple triple) {
if (triple.getSubject() instanceof BNode) {
return false;
}
if (triple.getObject() instanceof BNode) {
return false;
}
return true;
}
/** retrun triples with a bnode only at object position
*
* @param triples
* @return
*/
private static Triple getTripleWithBNodeObject(TripleCollection triples) {
for (Triple triple : triples) {
if (triple.getSubject() instanceof BNode) {
continue;
}
if (triple.getObject() instanceof BNode) {
return triple;
}
}
return null;
}
private static Triple getTripleWithBNodeSubject(TripleCollection triples) {
for (Triple triple : triples) {
if (triple.getSubject() instanceof BNode) {
return triple;
}
}
return null;
}
public static class NoSuchSubGraphException extends Exception {
}
}