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Stanford Parser processes raw text in English, Chinese, German, Arabic, and French, and extracts constituency parse trees.
package edu.stanford.nlp.parser.shiftreduce;
import java.io.PrintWriter;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.PriorityQueue;
import edu.stanford.nlp.ling.HasWord;
import edu.stanford.nlp.ling.Label;
import edu.stanford.nlp.ling.Sentence;
import edu.stanford.nlp.parser.KBestViterbiParser;
import edu.stanford.nlp.parser.common.ParserConstraint;
import edu.stanford.nlp.parser.common.ParserQuery;
import edu.stanford.nlp.parser.lexparser.Debinarizer;
import edu.stanford.nlp.trees.Tree;
import edu.stanford.nlp.util.Generics;
import edu.stanford.nlp.util.ScoredComparator;
import edu.stanford.nlp.util.ScoredObject;
public class ShiftReduceParserQuery implements ParserQuery {
Debinarizer debinarizer = new Debinarizer(false);
List originalSentence;
State initialState, finalState;
Tree debinarized;
boolean success;
boolean unparsable;
List bestParses;
final ShiftReduceParser parser;
List constraints = null;
public ShiftReduceParserQuery(ShiftReduceParser parser) {
this.parser = parser;
}
@Override
public boolean parse(List sentence) {
this.originalSentence = sentence;
initialState = ShiftReduceParser.initialStateFromTaggedSentence(sentence);
return parseInternal();
}
public boolean parse(Tree tree) {
this.originalSentence = tree.yieldHasWord();
initialState = ShiftReduceParser.initialStateFromGoldTagTree(tree);
return parseInternal();
}
private boolean parseInternal() {
final int maxBeamSize = Math.max(parser.op.testOptions().beamSize, 1);
success = true;
unparsable = false;
PriorityQueue beam = new PriorityQueue(maxBeamSize + 1, ScoredComparator.ASCENDING_COMPARATOR);
beam.add(initialState);
// TODO: don't construct as many PriorityQueues
while (beam.size() > 0) {
// System.err.println("================================================");
// System.err.println("Current beam:");
// System.err.println(beam);
PriorityQueue oldBeam = beam;
beam = new PriorityQueue(maxBeamSize + 1, ScoredComparator.ASCENDING_COMPARATOR);
State bestState = null;
for (State state : oldBeam) {
Collection> predictedTransitions = parser.model.findHighestScoringTransitions(state, true, maxBeamSize, constraints);
// System.err.println("Examining state: " + state);
for (ScoredObject predictedTransition : predictedTransitions) {
Transition transition = parser.model.transitionIndex.get(predictedTransition.object());
State newState = transition.apply(state, predictedTransition.score());
// System.err.println(" Transition: " + transition + " (" + predictedTransition.score() + ")");
if (bestState == null || bestState.score() < newState.score()) {
bestState = newState;
}
beam.add(newState);
if (beam.size() > maxBeamSize) {
beam.poll();
}
}
}
if (beam.size() == 0) {
// Oops, time for some fallback plan
// This can happen with the set of constraints given by the original paper
// For example, one particular French model had a situation where it would reach
// @Ssub @Ssub .
// without a left(Ssub) transition, so finishing the parse was impossible.
// This will probably result in a bad parse, but at least it
// will result in some sort of parse.
for (State state : oldBeam) {
Transition transition = parser.model.findEmergencyTransition(state, constraints);
if (transition != null) {
State newState = transition.apply(state);
if (bestState == null || bestState.score() < newState.score()) {
bestState = newState;
}
beam.add(newState);
}
}
}
// bestState == null only happens when we have failed to make progress, so quit
// If the bestState is finished, we are done
if (bestState == null || bestState.isFinished()) {
break;
}
}
if (beam.size() == 0) {
success = false;
unparsable = true;
debinarized = null;
finalState = null;
bestParses = Collections.emptyList();
} else {
// TODO: filter out beam elements that aren't finished
bestParses = Generics.newArrayList(beam);
Collections.sort(bestParses, beam.comparator());
Collections.reverse(bestParses);
finalState = bestParses.get(0);
debinarized = debinarizer.transformTree(finalState.stack.peek());
}
return success;
}
/**
* TODO: if we add anything interesting to report, we should report it here
*/
@Override
public boolean parseAndReport(List sentence, PrintWriter pwErr) {
boolean success = parse(sentence);
//System.err.println(getBestTransitionSequence());
//System.err.println(getBestBinarizedParse());
return success;
}
public Tree getBestBinarizedParse() {
return finalState.stack.peek();
}
public List getBestTransitionSequence() {
return finalState.transitions.asList();
}
@Override
public double getPCFGScore() {
return finalState.score;
}
@Override
public Tree getBestParse() {
return debinarized;
}
/** TODO: can we get away with not calling this PCFG? */
@Override
public Tree getBestPCFGParse() {
return debinarized;
}
@Override
public Tree getBestDependencyParse(boolean debinarize) {
return null;
}
@Override
public Tree getBestFactoredParse() {
return null;
}
/** TODO: if this is a beam, return all equal parses */
@Override
public List> getBestPCFGParses() {
ScoredObject parse = new ScoredObject(debinarized, finalState.score);
return Collections.singletonList(parse);
}
@Override
public boolean hasFactoredParse() {
return false;
}
/** TODO: return more if this used a beam */
@Override
public List> getKBestPCFGParses(int kbestPCFG) {
ScoredObject parse = new ScoredObject(debinarized, finalState.score);
return Collections.singletonList(parse);
}
@Override
public List> getKGoodFactoredParses(int kbest) {
throw new UnsupportedOperationException();
}
@Override
public KBestViterbiParser getPCFGParser() {
// TODO: find some way to treat this as a KBestViterbiParser?
return null;
}
@Override
public KBestViterbiParser getDependencyParser() {
return null;
}
@Override
public KBestViterbiParser getFactoredParser() {
return null;
}
@Override
public void setConstraints(List constraints) {
this.constraints = constraints;
}
@Override
public boolean saidMemMessage() {
return false;
}
@Override
public boolean parseSucceeded() {
return success;
}
/** TODO: skip sentences which are too long */
@Override
public boolean parseSkipped() {
return false;
}
@Override
public boolean parseFallback() {
return false;
}
/** TODO: add memory handling? */
@Override
public boolean parseNoMemory() {
return false;
}
@Override
public boolean parseUnparsable() {
return unparsable;
}
@Override
public List originalSentence() {
return originalSentence;
}
/**
* TODO: clearly this should be a default method in ParserQuery once Java 8 comes out
*/
@Override
public void restoreOriginalWords(Tree tree) {
if (originalSentence == null || tree == null) {
return;
}
List leaves = tree.getLeaves();
if (leaves.size() != originalSentence.size()) {
throw new IllegalStateException("originalWords and sentence of different sizes: " + originalSentence.size() + " vs. " + leaves.size() +
"\n Orig: " + Sentence.listToString(originalSentence) +
"\n Pars: " + Sentence.listToString(leaves));
}
// TODO: get rid of this cast
Iterator wordsIterator = (Iterator) originalSentence.iterator();
for (Tree leaf : leaves) {
leaf.setLabel(wordsIterator.next());
}
}
}