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Stanford CoreNLP provides a set of natural language analysis tools which can take raw English language text input and give the base forms of words, their parts of speech, whether they are names of companies, people, etc., normalize dates, times, and numeric quantities, mark up the structure of sentences in terms of phrases and word dependencies, and indicate which noun phrases refer to the same entities. It provides the foundational building blocks for higher level text understanding applications.

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package edu.stanford.nlp.parser.lexparser;

import java.util.*;

import edu.stanford.nlp.util.Index;
import edu.stanford.nlp.stats.ClassicCounter;
import edu.stanford.nlp.trees.Tree;


/** Gathers statistics on tree dependencies and then passes them to an
 *  MLEDependencyGrammar for dependency grammar construction.
 *
 *  @author Dan Klein
 */
public class MLEDependencyGrammarExtractor extends AbstractTreeExtractor {

  protected final Index wordIndex;
  protected final Index tagIndex;

  /** This is where all dependencies are stored (using full tag space). */
  protected ClassicCounter dependencyCounter = new ClassicCounter<>();
  //private Set dependencies = new HashSet();

  protected TreebankLangParserParams tlpParams;

  /** Whether left and right is distinguished. */
  protected boolean directional;

  /** Whether dependent distance from head is distinguished. */
  protected boolean useDistance;

  /** Whether dependent distance is distinguished more coarsely. */
  protected boolean useCoarseDistance;

  /** Whether basic category tags are in the dependency grammar. */
  protected final boolean basicCategoryTagsInDependencyGrammar;

  public MLEDependencyGrammarExtractor(Options op, Index wordIndex, Index tagIndex) {
    super(op);
    this.wordIndex = wordIndex;
    this.tagIndex = tagIndex;
    tlpParams = op.tlpParams;
    directional = op.directional;
    useDistance = op.distance;
    useCoarseDistance = op.coarseDistance;
    basicCategoryTagsInDependencyGrammar = op.trainOptions.basicCategoryTagsInDependencyGrammar;
  }

  @Override
  protected void tallyRoot(Tree lt, double weight) {
    // this list is in full (not reduced) tag space
    List deps = MLEDependencyGrammar.treeToDependencyList(lt, wordIndex, tagIndex);
    for (IntDependency dependency : deps) {
      dependencyCounter.incrementCount(dependency, weight);
    }
  }

  @Override
  public DependencyGrammar formResult() {
    wordIndex.addToIndex(Lexicon.UNKNOWN_WORD);
    MLEDependencyGrammar dg = new MLEDependencyGrammar(tlpParams, directional, useDistance, useCoarseDistance, basicCategoryTagsInDependencyGrammar, op, wordIndex, tagIndex);
    for (IntDependency dependency : dependencyCounter.keySet()) {
      dg.addRule(dependency, dependencyCounter.getCount(dependency));
    }
    return dg;
  }

} // end class MLEDependencyGrammarExtractor