package edu.stanford.nlp.trees;
import edu.stanford.nlp.ling.HasCategory;
import edu.stanford.nlp.ling.HasTag;
import edu.stanford.nlp.ling.HasWord;
import edu.stanford.nlp.ling.Label;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
/**
* Implements a 'semantic head' variant of the the HeadFinder found
* in Michael Collins' 1999 thesis.
* This version chooses the semantic head verb rather than the verb form
* for cases with verbs. And it makes similar themed changes to other
* categories: e.g., in question phrases, like "Which Brazilian game", the
* head is made "game" not "Which" as in common PTB head rules.<p/>
* <p/>
* By default the SemanticHeadFinder uses a treatment of copula where the
* complement of the copula is taken as the head. That is, a sentence like
* "Bill is big" will be analyzed as <p/>
* <p/>
* <code>nsubj</code>(big, Bill) <br/>
* <code>cop</code>(big, is) <p/>
* <p/>
* This analysis is used for questions and declaratives for adjective
* complements and declarative nominal complements. However Wh-sentences
* with nominal complements do not receive this treatment.
* "Who is the president?" is analyzed with "the president" as nsubj and "who"
* as "attr" of the copula:<p/><p>
* <code>nsubj</code>(is, president)<br/>
* <code>attr</code>(is, Who) <p/>
* <p/>
* (Such nominal copula sentences are complex: arguably, depending on the
* circumstances, several analyses are possible, with either the overt NP able
* to be any of the subject, the predicate, or one of two referential entities
* connected by an equational copula. These uses aren't differentiated.)
* <p/>
* Existential sentences are treated as follows: <br/>
* "There is a man" <br/>
* <code>expl</code>(is, There) <br/>
* <code>det</code>(man-4, a-3) <br/>
* <code>nsubj</code>(is-2, man-4)<br/>
*
* @author John Rappaport
* @author Marie-Catherine de Marneffe
* @author Anna Rafferty
*/
public class SemanticHeadFinder extends ModCollinsHeadFinder {
private static final boolean DEBUG = false;
private static final String[] auxiliaries = {"will", "wo", "shall", "sha", "may", "might", "should", "would", "can", "could", "ca", "must", "has", "have", "had", "having", "get", "gets", "getting", "got", "gotten", "do", "does", "did", "to", "'ve", "'d", "'ll"};
private static final String[] beGetVerbs = {"be", "being", "been", "am", "are", "is", "was", "were", "'m", "'re", "'s", "s", "get", "getting", "gets", "got"};
private static final String[] copulaVerbs = {"be", "being", "been", "am", "are", "is", "was", "were", "'m", "'re", "'s", "s", "seem", "seems", "seemed", "appear", "appears", "appeared", "stay", "stays", "stayed", "remain", "remains", "remained", "resemble", "resembles", "resembled", "become", "becomes", "became"};
private static final String[] verbTags = {"TO", "MD", "VB", "VBD", "VBP", "VBZ", "VBG", "VBN", "AUX", "AUXG"};
private final HashSet<String> verbalAuxiliaries;
private final HashSet<String> copulars;
private final HashSet<String> passiveAuxiliaries;
private final HashSet<String> verbalTags;
public SemanticHeadFinder() {
this(new PennTreebankLanguagePack(), true);
}
public SemanticHeadFinder(boolean cop) {
this(new PennTreebankLanguagePack(), cop);
}
/** Create a SemanticHeadFinder.
*
* @param tlp The TreebankLanguagePack, used by the superclass to get basic
* category of constituents.
* @param cop If true, a copular verb (be, seem, appear, stay, remain, resemble, become)
* is not treated as head when it has an AdjP or NP complement. If false,
* a copula verb is still always treated as a head. But it will still
* be treated as an auxiliary in periphrastic tenses with a VP complement.
*/
public SemanticHeadFinder(TreebankLanguagePack tlp, boolean cop) {
super(tlp);
ruleChanges();
// make a distinction between auxiliaries and copula verbs to
// get the NP has semantic head in sentences like "Bill is an honest man". (Added "sha" for "shan't" May 2009
verbalAuxiliaries = new HashSet<String>();
verbalAuxiliaries.addAll(Arrays.asList(auxiliaries));
passiveAuxiliaries = new HashSet<String>();
passiveAuxiliaries.addAll(Arrays.asList(beGetVerbs));
//copula verbs having an NP complement
copulars = new HashSet<String>();
if (cop) {
copulars.addAll(Arrays.asList(copulaVerbs));
} // a few times the apostrophe is missing on "'s"
verbalTags = new HashSet<String>();
// include Charniak tags so can do BLLIP right
verbalTags.addAll(Arrays.asList(verbTags));
}
//makes modifications of Collins' rules to better fit with semantic notions of heads
private void ruleChanges() {
// NP: don't want a POS to be the head
nonTerminalInfo.put("NP", new String[][]{{"rightdis", "NN", "NNP", "NNPS", "NNS", "NX", "NML", "JJR"}, {"left", "NP", "PRP"}, {"rightdis", "$", "ADJP", "FW"}, {"right", "CD"}, {"rightdis", "JJ", "JJS", "QP", "DT", "WDT", "NML", "PRN", "RB", "RBR", "ADVP"}, {"left", "POS"}, rightExceptPunct});
// WHNP clauses should have the same sort of head as an NP
// but it a WHNP has a NP and a WHNP under it, the WHNP should be the head. E.g., (WHNP (WHNP (WP$ whose) (JJ chief) (JJ executive) (NN officer))(, ,) (NP (NNP James) (NNP Gatward))(, ,))
nonTerminalInfo.put("WHNP", new String[][]{{"rightdis", "NN", "NNP", "NNPS", "NNS", "NX", "NML", "JJR", "WP"}, {"left", "WHNP", "NP"}, {"rightdis", "$", "ADJP", "PRN", "FW"}, {"right", "CD"}, {"rightdis", "JJ", "JJS", "RB", "QP"}, {"left", "WHPP", "WHADJP", "WP$", "WDT"}});
//WHADJP
nonTerminalInfo.put("WHADJP", new String[][]{{"left", "ADJP", "JJ", "JJR"}, {"right", "RB"}, rightExceptPunct});
//WHADJP
nonTerminalInfo.put("WHADVP", new String[][]{{"rightdis", "WRB", "WHADVP", "RB", "JJ"}, rightExceptPunct}); // if not WRB or WHADVP, probably has flat NP structure, allow JJ for "how long" constructions
// QP: we don't want the first CD to be the semantic head (e.g., "three billion": head should be "billion"), so we go from right to left
nonTerminalInfo.put("QP", new String[][]{{"right", "$", "NNS", "NN", "CD", "JJ", "PDT", "DT", "IN", "RB", "NCD", "QP", "JJR", "JJS"}});
// S, SBAR and SQ clauses should prefer the main verb as the head
// S: "He considered him a friend" -> we want a friend to be the head
nonTerminalInfo.put("S", new String[][]{{"left", "VP", "S", "FRAG", "SBAR", "ADJP", "UCP", "TO"}, {"right", "NP"}});
nonTerminalInfo.put("SBAR", new String[][]{{"left", "S", "SQ", "SINV", "SBAR", "FRAG", "VP", "WHNP", "WHPP", "WHADVP", "WHADJP", "IN", "DT"}});
// VP shouldn't be needed in SBAR, but occurs in one buggy tree in PTB3 wsj_1457 and otherwise does no harm
nonTerminalInfo.put("SQ", new String[][]{{"left", "VP", "SQ", "ADJP", "VB", "VBZ", "VBD", "VBP", "MD", "AUX", "AUXG"}});
// UCP take the first element as head
nonTerminalInfo.put("UCP", new String[][]{leftExceptPunct});
// CONJP: we want different heads for "but also" and "but not" and we don't want "not" to be the head in "not to mention"; now make "mention" head of "not to mention"
nonTerminalInfo.put("CONJP", new String[][]{{"right", "VB", "JJ", "RB", "IN", "CC"}, rightExceptPunct});
// FRAG: crap rule needs to be change if you want to parse glosses
nonTerminalInfo.put("FRAG", new String[][]{{"left", "IN"}, {"right", "RB"}, {"left", "NP"}, {"left", "ADJP", "ADVP", "FRAG", "S", "SBAR", "VP"}, leftExceptPunct});
// PP first word (especially in coordination of PPs)
nonTerminalInfo.put("PP", new String[][]{{"right", "IN", "TO", "VBG", "VBN", "RP", "FW", "JJ"}, {"left", "PP"}});
// PRN: sentence first
nonTerminalInfo.put("PRN", new String[][]{{"left", "VP", "SQ", "S", "SINV", "SBAR", "NP", "ADJP", "PP", "ADVP", "INTJ", "WHNP", "NAC", "VBP", "JJ", "NN", "NNP"}, leftExceptPunct});
// add the constituent XS (special node to add a layer in a QP tree introduced in our QPTreeTransformer)
nonTerminalInfo.put("XS", new String[][]{{"right", "IN"}});
}
/**
* Overwrite the postOperationFix method: a, b and c -> we want a to be the head
*/
@Override
protected int postOperationFix(int headIdx, Tree[] daughterTrees) {
if (headIdx >= 2) {
String prevLab = tlp.basicCategory(daughterTrees[headIdx - 1].value());
if (prevLab.equals("CC") || prevLab.equals("CONJP")) {
int newHeadIdx = headIdx - 2;
Tree t = daughterTrees[newHeadIdx];
while (newHeadIdx >= 0 && t.isPreTerminal() && tlp.isPunctuationTag(t.value())) {
newHeadIdx--;
}
while (newHeadIdx >= 2 && tlp.isPunctuationTag(daughterTrees[newHeadIdx - 1].value())) {
newHeadIdx = newHeadIdx - 2;
}
if (newHeadIdx >= 0) {
headIdx = newHeadIdx;
}
}
}
return headIdx;
}
/**
* Determine which daughter of the current parse tree is the
* head. It assumes that the daughters already have had their
* heads determined. Uses special rule for VP heads
*
* @param t The parse tree to examine the daughters of.
* This is assumed to never be a leaf
* @return The parse tree that is the head
*/
@Override
protected Tree determineNonTrivialHead(Tree t, Tree parent) {
String motherCat = tlp.basicCategory(t.label().value());
if (DEBUG) {
System.err.println("At " + motherCat + ", my parent is " + parent);
}
// do VPs with auxiliary as special case
if ((motherCat.equals("VP") || motherCat.equals("SQ") || motherCat.equals("SINV"))) {
Tree[] kids = t.children();
// try to find if there is an auxiliary verb
if (DEBUG) {
System.err.println("Semantic head finder: at VP");
System.err.println("Class is " + t.getClass().getName());
t.pennPrint(System.err);
//System.err.println("hasVerbalAuxiliary = " + hasVerbalAuxiliary(kids, verbalAuxiliaries));
}
// looks for auxiliaries
if (hasVerbalAuxiliary(kids, verbalAuxiliaries) || hasPassiveProgressiveAuxiliary(kids, passiveAuxiliaries)) {
// String[] how = new String[] {"left", "VP", "ADJP", "NP"};
// Including NP etc seems okay for copular sentences but is
// problematic for other auxiliaries, like 'he has an answer'
// But maybe doing ADJP is fine!
String[] how = new String[]{"left", "VP", "ADJP"};
Tree pti = traverseLocate(kids, how, false);
if (DEBUG) {
System.err.println("Determined head (case 1) for " + t.value() + " is: " + pti);
}
if (pti != null) {
return pti;
} else {
// System.err.println("------");
// System.err.println("SemanticHeadFinder failed to reassign head for");
// t.pennPrint(System.err);
// System.err.println("------");
}
}
// looks for copular verbs
if (hasVerbalAuxiliary(kids, copulars) && ! isExistential(t, parent) && ! isWHQ(t, parent)) {
String[] how;
if (motherCat.equals("SQ")) {
how = new String[]{"right", "VP", "ADJP", "NP", "WHADJP", "WHNP"};
} else {
how = new String[]{"left", "VP", "ADJP", "NP", "WHADJP", "WHNP"};
}
Tree pti = traverseLocate(kids, how, false);
// don't allow a temporal to become head
if (pti != null && pti.label() != null && pti.label().value().contains("-TMP")) {
pti = null;
}
// In SQ, only allow an NP to become head if there is another one to the left (then it's probably predicative)
if (motherCat.equals("SQ") && pti != null && pti.label() != null && pti.label().value().startsWith("NP")) {
boolean foundAnotherNp = false;
for (Tree kid : kids) {
if (kid == pti) {
break;
} else if (kid.label() != null && kid.label().value().startsWith("NP")) {
foundAnotherNp = true;
break;
}
}
if ( ! foundAnotherNp) {
pti = null;
}
}
if (DEBUG) {
System.err.println("Determined head (case 2) for " + t.value() + " is: " + pti);
}
if (pti != null) {
return pti;
} else {
if (DEBUG) {
System.err.println("------");
System.err.println("SemanticHeadFinder failed to reassign head for");
t.pennPrint(System.err);
System.err.println("------");
}
}
}
}
Tree hd = super.determineNonTrivialHead(t, parent);
if (DEBUG) {
System.err.println("Determined head (case 3) for " + t.value() + " is: " + hd);
}
return hd;
}
/* Checks whether the tree t is an existential constituent
* There are two cases:
* -- affirmative sentences in which "there" is a left sister of the VP
* -- questions in which "there" is a daughter of the SQ.
*
*/
private boolean isExistential(Tree t, Tree parent) {
if (DEBUG) {
System.err.println("isExistential: " + t + ' ' + parent);
}
boolean toReturn = false;
String motherCat = tlp.basicCategory(t.label().value());
// affirmative case
if (motherCat.equals("VP") && parent != null) {
//take t and the sisters
Tree[] kids = parent.children();
// iterate over the sisters before t and checks if existential
for (Tree kid : kids) {
if (!kid.value().equals("VP")) {
List<Label> tags = kid.preTerminalYield();
for (Label tag : tags) {
if (tag.value().equals("EX")) {
toReturn = true;
}
}
} else {
break;
}
}
}
// question case
else if (motherCat.startsWith("SQ") && parent != null) {
//take the daughters
Tree[] kids = parent.children();
// iterate over the daughters and checks if existential
for (Tree kid : kids) {
if (!kid.value().startsWith("VB")) {//not necessary to look into the verb
List<Label> tags = kid.preTerminalYield();
for (Label tag : tags) {
if (tag.value().equals("EX")) {
toReturn = true;
}
}
}
}
}
if (DEBUG) {
System.err.println("decision " + toReturn);
}
return toReturn;
}
/* Is the tree t a WH-question?
* At present this is only true if the tree t is a SQ having a WH.* sister
* and headed by a SBARQ.
* (It was changed to looser definition in Feb 2006.)
*
*/
private static boolean isWHQ(Tree t, Tree parent) {
if (t == null) {
return false;
}
boolean toReturn = false;
if (t.value().startsWith("SQ")) {
if (parent != null && parent.value().equals("SBARQ")) {
Tree[] kids = parent.children();
for (Tree kid : kids) {
// looks for a WH.*
if (kid.value().startsWith("WH")) {
toReturn = true;
}
}
}
}
if (DEBUG) {
System.err.println("in isWH, decision: " + toReturn + " for node " + t);
}
return toReturn;
}
// now overally complex so it deals with coordinations. Maybe change this class to use tregrex?
private boolean hasPassiveProgressiveAuxiliary(Tree[] kids, HashSet<String> verbalSet) {
if (DEBUG) {
System.err.println("Checking for passive/progressive auxiliary");
}
boolean foundPassiveVP = false;
boolean foundPassiveAux = false;
for (Tree kid : kids) {
if (DEBUG) {
System.err.println(" checking in " + kid);
}
if (kid.isPreTerminal()) {
Label kidLabel = kid.label();
String tag = null;
if (kidLabel instanceof HasTag) {
tag = ((HasTag) kidLabel).tag();
}
if (tag == null) {
tag = kid.value();
}
Label wordLabel = kid.firstChild().label();
String word = null;
if (wordLabel instanceof HasWord) {
word = ((HasWord) wordLabel).word();
}
if (word == null) {
word = wordLabel.value();
}
if (DEBUG) {
System.err.println("Checking " + kid.value() + " head is " + word + '/' + tag);
}
String lcWord = word.toLowerCase();
if (verbalTags.contains(tag) && verbalSet.contains(lcWord)) {
if (DEBUG) {
System.err.println("hasPassiveProgressiveAuxiliary found passive aux");
}
foundPassiveAux = true;
}
} else if (kid.isPhrasal()) {
Label kidLabel = kid.label();
String cat = null;
if (kidLabel instanceof HasCategory) {
cat = ((HasCategory) kidLabel).category();
}
if (cat == null) {
cat = kid.value();
}
if ( ! cat.startsWith("VP")) {
continue;
}
if (DEBUG) {
System.err.println("hasPassiveProgressiveAuxiliary found VP");
}
Tree[] kidkids = kid.children();
boolean foundParticipleInVp = false;
for (Tree kidkid : kidkids) {
if (DEBUG) {
System.err.println(" hasPassiveProgressiveAuxiliary examining " + kidkid);
}
if (kidkid.isPreTerminal()) {
Label kidkidLabel = kidkid.label();
String tag = null;
if (kidkidLabel instanceof HasTag) {
tag = ((HasTag) kidkidLabel).tag();
}
if (tag == null) {
tag = kidkid.value();
}
// we allow in VBD because of frequent tagging mistakes
if ("VBN".equals(tag) || "VBG".equals(tag) || "VBD".equals(tag)) {
foundPassiveVP = true;
if (DEBUG) {
System.err.println("hasPassiveAuxiliary found VBN/VBG/VBD VP");
}
break;
} else if ("CC".equals(tag) && foundParticipleInVp) {
foundPassiveVP = true;
if (DEBUG) {
System.err.println("hasPassiveAuxiliary [coordination] found (VP (VP[VBN/VBG/VBD] CC");
}
break;
}
} else if (kidkid.isPhrasal()) {
String catcat = null;
if (kidLabel instanceof HasCategory) {
catcat = ((HasCategory) kidLabel).category();
}
if (catcat == null) {
catcat = kid.value();
}
if ("VP".equals(catcat)) {
if (DEBUG) {
System.err.println("hasPassiveAuxiliary found (VP (VP)), recursing");
}
foundParticipleInVp = vpContainsParticiple(kidkid);
} else if (("CONJP".equals(catcat) || "PRN".equals(catcat)) && foundParticipleInVp) { // occasionally get PRN in CONJ-like structures
foundPassiveVP = true;
if (DEBUG) {
System.err.println("hasPassiveAuxiliary [coordination] found (VP (VP[VBN/VBG/VBD] CONJP");
}
break;
}
}
}
}
if (foundPassiveAux && foundPassiveVP) {
break;
}
} // end for (Tree kid : kids)
if (DEBUG) {
System.err.println("hasPassiveProgressiveAuxiliary returns " + (foundPassiveAux && foundPassiveVP));
}
return foundPassiveAux && foundPassiveVP;
}
private boolean vpContainsParticiple(Tree t) {
for (Tree kid : t.children()) {
if (DEBUG) {
System.err.println("vpContainsParticiple examining " + kid);
}
if (kid.isPreTerminal()) {
Label kidLabel = kid.label();
String tag = null;
if (kidLabel instanceof HasTag) {
tag = ((HasTag) kidLabel).tag();
}
if (tag == null) {
tag = kid.value();
}
if ("VBN".equals(tag) || "VBG".equals(tag) || "VBD".equals(tag)) {
if (DEBUG) {
System.err.println("vpContainsParticiple found VBN/VBG/VBD VP");
}
return true;
}
}
}
return false;
}
/**
* Reinserted so samples.GetSubcats compiles ... should rework if
* this is going to stay.
*
* @param t A tree to examine for being an auxiliary.
* @return Whether it is a verbal auxiliary (be, do, have, get)
*/
public boolean isVerbalAuxiliary(Tree t) {
Tree[] trees = new Tree[]{t};
return hasVerbalAuxiliary(trees, verbalAuxiliaries);
}
/** This looks to see whether any of the children is a preterminal headed by a word
* which is within the set verbalSet (which in practice is either
* auxiliary or copula verbs). It only returns true if it's a preterminal head, since
* you don't want to pick things up in phrasal daughters. That is an error.
*
* @param kids The child trees
* @param verbalSet The set of words
* @return Returns true if one of the child trees is a preterminal verb headed
* by a word in verbalSet
*/
private boolean hasVerbalAuxiliary(Tree[] kids, HashSet<String> verbalSet) {
if (DEBUG) {
System.err.println("Checking for verbal auxiliary");
}
for (Tree kid : kids) {
if (DEBUG) {
System.err.println(" checking in " + kid);
}
if (kid.isPreTerminal()) {
Label kidLabel = kid.label();
String tag = null;
if (kidLabel instanceof HasTag) {
tag = ((HasTag) kidLabel).tag();
}
if (tag == null) {
tag = kid.value();
}
Label wordLabel = kid.firstChild().label();
String word = null;
if (wordLabel instanceof HasWord) {
word = ((HasWord) wordLabel).word();
}
if (word == null) {
word = wordLabel.value();
}
if (DEBUG) {
System.err.println("Checking " + kid.value() + " head is " + word + '/' + tag);
}
String lcWord = word.toLowerCase();
if (verbalTags.contains(tag) && verbalSet.contains(lcWord)) {
if (DEBUG) {
System.err.println("hasVerbalAuxiliary returns true");
}
return true;
}
}
}
if (DEBUG) {
System.err.println("hasVerbalAuxiliary returns false");
}
return false;
}
private static final long serialVersionUID = 5721799188009249808L;
}