/*
* 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.jena.reasoner.transitiveReasoner;
import java.util.*;
import org.apache.jena.graph.* ;
import org.apache.jena.reasoner.transitiveReasoner.TransitiveGraphCache.* ;
import org.apache.jena.shared.BrokenException ;
import org.apache.jena.util.iterator.* ;
/**
* Inner class used to represent the graph node structure.
* Rather fat nodes (four sets)
*/
class GraphNode {
/** The RDF Graph Node this corresponds to */
protected Node rdfNode;
/** The list of direct successor nodes to this node */
protected Set<GraphNode> succ = new HashSet<>();
/** The list of direct predecessors nodes */
protected Set<GraphNode> pred = new HashSet<>();
/** The set of all transitive successor nodes to this node */
protected Set<GraphNode> succClosed = new HashSet<>();
/** An optional cache of the triples that represent succClosed */
protected List<Triple> succClosedTriples;
/**
Plain Siblings for simple nodes. For the lead node in a SCC will be a Leader
with components containing all the nodes in the SCC. For non-lead nodes
it will be a Subordinate referring to the lead node.
*/
private Siblings siblings = new Siblings();
static class Siblings
{
Set<GraphNode> members()
{ throw new BrokenException( "cannot ask for components of a raw GraphNode" ); }
void addInto( Set<GraphNode> nodes, GraphNode m )
{ nodes.add( m ); }
void addSuccessors( Node base, TransitiveGraphCache tgc, ArrayList<Triple> result )
{}
static final NullIterator<GraphNode> noMembers = NullIterator.instance();
Iterator<GraphNode> siblingIterator()
{ return noMembers; }
GraphNode leadNode( GraphNode unlessSpecified )
{ return unlessSpecified; }
String dump()
{ return ""; }
}
static class Leader extends Siblings
{
final Set<GraphNode> components;
Leader( Set<GraphNode> components )
{ this.components = components; }
@Override Set<GraphNode> members()
{ return components; }
@Override void addInto( Set<GraphNode> nodes, GraphNode ignored )
{ nodes.addAll( components ); }
@Override void addSuccessors( Node base, TransitiveGraphCache tgc, ArrayList<Triple> result )
{
for ( GraphNode component : components )
{
result.add( new Triple( base, tgc.closedPredicate, component.rdfNode ) );
}
}
@Override Iterator<GraphNode> siblingIterator()
{ return components.iterator(); }
@Override String dump()
{ return " SCC=" + dumpSet( components ) +", "; }
}
static class Subordinate extends Siblings
{
final GraphNode leader;
Subordinate( GraphNode n )
{ leader = n; }
@Override Set<GraphNode> members()
{ throw new BrokenException( "cannot ask for components of a raw GraphNode" ); }
@Override GraphNode leadNode( GraphNode unlessSpecified )
{ return leader.leadNode(); }
@Override String dump()
{ return " leader=" + leader + ", "; }
}
// should only be called on a lead node
private Set<GraphNode> siblings()
{ return siblings.members(); }
private void addSiblings( Set<GraphNode> target, GraphNode m )
{ m.siblings.addInto( target, m ); }
/**
* Return the lead node in the strongly connected component containing this node.
* It will be the node itself if it is a singleton or the lead node.
*/
public GraphNode leadNode()
{ return siblings.leadNode( this ); }
public Iterator<GraphNode> siblingIterator()
{ return siblings.siblingIterator(); }
public Iterator<GraphNode> concatenateSiblings( Iterator<GraphNode> base )
{
return WrappedIterator.create( base ).andThen( siblings.siblingIterator() );
}
private void becomeSubordinateOf( GraphNode leader )
{ this.siblings = new Subordinate( leader ); }
private void becomeLeaderOf( Set<GraphNode> newSiblings )
{ this.siblings = new Leader( newSiblings ); }
/**
* Full dump for debugging
*/
public String dump() {
return
rdfNode.getLocalName()
+ siblings.dump()
+ " succ=" + dumpSet( succ )
+ ", succClose=" + dumpSet( succClosed )
+ ", pred=" + dumpSet( pred )
;
}
/**
* Constructor.
*/
public GraphNode(Node node) {
rdfNode = node;
}
/**
* Return true if there is a path from this node to the argument node.
*/
public boolean pathTo(GraphNode A) {
if (this == A) return true;
return succClosed.contains(A);
}
/**
* Return true if there is a direct path from this node to the argument node.
*/
public boolean directPathTo(GraphNode A) {
if (this == A) return true;
return succ.contains(A);
}
/**
* Visit each predecessor of this node applying the given visitor.
*/
public <Alpha, Beta> void visitPredecessors(Visitor<Alpha, Beta> visitor, Alpha arg1, Beta arg2) {
List<GraphNode> kill = visitor.visit(this, null, arg1, arg2);
if (kill != null) pred.removeAll(kill);
doVisitPredecessors(visitor, arg1, arg2, new HashSet<GraphNode>());
}
/**
* Visit each predecessor of this node applying the given visitor.
* Breadth first.
*/
private <Alpha, Beta> void doVisitPredecessors(Visitor<Alpha, Beta> visitor, Alpha arg1, Beta arg2, Set<GraphNode> seen) {
if (seen.add(this)) {
Collection<GraphNode> allKill = null;
for (Iterator<GraphNode> i = pred.iterator(); i.hasNext(); ) {
GraphNode pred = i.next();
List<GraphNode> kill = visitor.visit(pred, this, arg1, arg2);
if (kill != null) {
if (allKill == null) allKill = new ArrayList<GraphNode>();
allKill.addAll(kill);
}
}
if (allKill != null) pred.removeAll(allKill);
for (Iterator<GraphNode> i = pred.iterator(); i.hasNext(); ) {
GraphNode pred = i.next();
pred.doVisitPredecessors(visitor, arg1, arg2, seen);
}
}
}
/**
* Return an iterator over all the indirect successors of this node.
* This does NOT include aliases of successors and is used for graph maintenance.
*/
public Iterator<GraphNode> iteratorOverSuccessors() {
return succClosed.iterator();
}
/**
* Assert a direct link between this node and this given target.
* Does not update the closed successor cache
*/
public void assertLinkTo(GraphNode target) {
if (this == target) return;
succ.add(target);
target.pred.add(this);
clearTripleCache();
}
/**
* Remove a direct link currently from this node to the given target.
* Does not update the closed successor cache.
*/
public void retractLinkTo(GraphNode target) {
if (this == target) return;
succ.remove(target);
target.pred.remove(this);
clearTripleCache();
}
/**
* Assert an inferred indirect link from this node to the given traget
*/
public void assertIndirectLinkTo(GraphNode target) {
// if (this == target) return;
succClosed.add(target);
clearTripleCache();
}
/**
* Clear the option cache of the closure triples.
*/
public void clearTripleCache() {
succClosedTriples = null;
}
/**
* Propagate the results of adding a link from this
* node to the target node.
*/
public void propagateAdd(GraphNode target) {
Set<GraphNode> sc = new HashSet<>(target.succClosed);
sc.add(target);
visitPredecessors(new Visitor<Set<GraphNode>, GraphNode>() {
@Override
public List<GraphNode> visit(GraphNode node, GraphNode processing, Set<GraphNode> sc, GraphNode target) {
// Add closure
node.succClosed.addAll( sc );
// Scan for redundant links
List<GraphNode> kill = null;
for (Iterator<GraphNode> i = node.succ.iterator(); i.hasNext();) {
GraphNode s = i.next();
if (sc.contains(s)) {
i.remove();
if (s == processing) {
// Can't remove immediately w/o beaking the visitor loop
if (kill == null) kill = new ArrayList<>();
kill.add(node);
} else {
s.pred.remove(node);
}
}
}
return kill;
}
}, sc, target);
}
/**
* Propagate the results of creating a new SCC with this
* node as lead.
*/
public void propagateSCC() {
Set<GraphNode> visited = new HashSet<>();
visited.add(this);
// Scan predecessors not including ourselves
doVisitPredecessors(new Visitor<Set<GraphNode>, Object>() {
@Override
public List<GraphNode> visit(GraphNode node, GraphNode processing, Set<GraphNode> sc, Object ignored ) {
// Add closure
node.succClosed.addAll(sc);
// Scan for redundant links
List<GraphNode> kill = null;
for (Iterator<GraphNode> i = node.succ.iterator(); i.hasNext();) {
GraphNode s = i.next();
if (sc.contains(s)) {
i.remove();
// s.pred.remove(node);
if (s == processing) {
// Can't remove immediately w/o beaking the visitor loop
if (kill == null) kill = new ArrayList<>();
kill.add(node);
} else {
s.pred.remove(node);
}
}
}
return kill;
}
}, succClosed, null, visited);
}
/**
* Given a set of SCC nodes make this the lead member of the SCC and
* reroute all incoming and outgoing links accordingly.
* This eager rewrite is based on the assumption that there are few cycles
* so it is better to rewrite once and keep the graph easy to traverse.
*/
public void makeLeadNodeFor(Set<GraphNode> members) {
// Accumulate all successors
Set<GraphNode> newSucc = new HashSet<>();
Set<GraphNode> newSuccClosed = new HashSet<>();
for ( GraphNode n : members )
{
newSucc.addAll( n.succ );
newSuccClosed.addAll( n.succClosed );
}
newSucc.removeAll(members);
newSuccClosed.removeAll(members);
succ = newSucc;
succClosed = newSuccClosed;
// Rewrite all direct successors to have us as predecessor
for ( GraphNode n : succ )
{
n.pred.removeAll( members );
n.pred.add( this );
}
// Find all predecessor nodes and relink link them to point to us
Set<GraphNode> done = new HashSet<>();
Set<GraphNode> newAliases = new HashSet<>();
for ( GraphNode member : members )
{
addSiblings( newAliases, member );
}
becomeLeaderOf( newAliases );
for ( GraphNode n : members )
{
if ( n != this )
{
pred.addAll( n.pred );
n.relocateAllRefTo( this, done );
n.becomeSubordinateOf( this );
}
}
pred.removeAll(members);
}
/**
* This node is being absorbed into an SCC with the given node as the
* new lead node. Trace out all predecessors to this node and relocate
* them to point to the new lead node.
*/
private void relocateAllRefTo(GraphNode lead, Set<GraphNode> done) {
visitPredecessors(new Visitor<Set<GraphNode>, GraphNode>(){
@Override
public List<GraphNode> visit(GraphNode node, GraphNode processing, Set<GraphNode> done, GraphNode leadIn) {
if (done.add( node )) {
Set<GraphNode> members = leadIn.siblings();
int before = node.succ.size();
node.succ.removeAll(members);
node.succClosed.removeAll(members);
node.succClosed.add(leadIn);
if (node.succ.size() != before) {
node.succ.add(leadIn);
}
}
return null;
}
}, done, lead);
}
/**
* Return an iterator over all of the triples representing outgoing links
* from this node.
* @param closed if set to true it returns triples in the transitive closure,
* if set to false it returns triples in the transitive reduction
* @param tgc the enclosing TransitiveGraphCache
*/
public ExtendedIterator<Triple> listTriples(boolean closed, TransitiveGraphCache tgc) {
if (tgc.cacheTriples) {
// TODO implement - for now default to non-cached
return WrappedIterator.create(leadNode().triplesForSuccessors(rdfNode, closed, tgc).iterator());
} else {
return WrappedIterator.create(leadNode().triplesForSuccessors(rdfNode, closed, tgc).iterator());
}
}
/**
* Create a list of triples for a given set of successors to this node.
*/
private List<Triple> triplesForSuccessors(Node base, boolean closed, TransitiveGraphCache tgc) {
Set<GraphNode> successors = closed ? succClosed : succ;
ArrayList<Triple> result = new ArrayList<>(successors.size() + 10);
result.add(new Triple(base, tgc.closedPredicate, base)); // implicit reflexive case
for ( GraphNode s : successors )
{
result.add( new Triple( base, tgc.closedPredicate, s.rdfNode ) );
s.siblings.addSuccessors( base, tgc, result );
}
siblings.addSuccessors( base, tgc, result );
return result;
}
/**
* Return an iterator over all of the triples representing incoming links to this node.
* Currently no caching enabled.
*/
public ExtendedIterator<Triple> listPredecessorTriples(boolean closed, TransitiveGraphCache tgc) {
return new GraphWalker(leadNode(), rdfNode, closed, tgc.closedPredicate);
}
/**
* Print node label to assist with debug.
*/
@Override public String toString() {
return "[" + rdfNode.getLocalName() + "]";
}
/**
* Dump a set to a string for debug.
*/
private static String dumpSet(Set<GraphNode> s) {
StringBuffer sb = new StringBuffer();
sb.append("{");
boolean started = false;
for ( GraphNode value : s )
{
if ( started )
{
sb.append( ", " );
}
else
{
started = true;
}
sb.append( value.toString() );
}
sb.append("}");
return sb.toString();
}
}