/**
*
* Copyright 1999-2012 Carnegie Mellon University.
* Portions Copyright 2002 Sun Microsystems, Inc.
* Portions Copyright 2002 Mitsubishi Electric Research Laboratories.
* All Rights Reserved. Use is subject to license terms.
*
* See the file "license.terms" for information on usage and
* redistribution of this file, and for a DISCLAIMER OF ALL
* WARRANTIES.
*
*/
package edu.cmu.sphinx.linguist.g2p;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.regex.Pattern;
import edu.cmu.sphinx.fst.Arc;
import edu.cmu.sphinx.fst.Fst;
import edu.cmu.sphinx.fst.ImmutableFst;
import edu.cmu.sphinx.fst.State;
import edu.cmu.sphinx.fst.operations.ArcSort;
import edu.cmu.sphinx.fst.operations.Compose;
import edu.cmu.sphinx.fst.operations.ILabelCompare;
import edu.cmu.sphinx.fst.operations.NShortestPaths;
import edu.cmu.sphinx.fst.operations.OLabelCompare;
import edu.cmu.sphinx.fst.operations.Project;
import edu.cmu.sphinx.fst.operations.ProjectType;
import edu.cmu.sphinx.fst.operations.RmEpsilon;
import edu.cmu.sphinx.fst.semiring.Semiring;
import edu.cmu.sphinx.fst.semiring.TropicalSemiring;
import edu.cmu.sphinx.fst.utils.Utils;
/**
* The grapheme-to-phoneme (g2p) decoder
*
* @author John Salatas
*/
public class G2PConverter {
// epsilon symbol
String eps = "<eps>";
// end sequence symbol
String se = "</s>";
// begin sequence symbol
String sb = "<s>";
// skip symbol
String skip = "_";
// separator symbol
String tie = "|";
// set containing sequences to ignore
HashSet<String> skipSeqs = new HashSet<String>();
// clusters
ArrayList<String>[] clusters = null;
// the g2p model
ImmutableFst g2pmodel;
// fst containing the epsilon filter for the compose operation
Fst epsilonFilter;
/**
* Create a decoder by loading the serialized model from a specified URL
*
* @param g2pModelUrl
* the URL of the serialized model
* @throws IOException when model is not loaded
*/
public G2PConverter(URL g2pModelUrl) throws IOException {
try {
g2pmodel = ImmutableFst.loadModel(g2pModelUrl.openStream());
} catch (ClassNotFoundException e) {
throw new IOException("Failed to load the model from " + g2pModelUrl, e);
}
init();
}
/**
* Create a decoder by loading the serialized model from a specified
* filename
*
* @param g2pmodel_file
* the filename of the serialized model
*/
public G2PConverter(String g2pmodel_file) {
g2pmodel = ImmutableFst.loadModel(g2pmodel_file);
init();
}
/**
* Initialize the decoder
*/
private void init() {
skipSeqs.add(eps);
skipSeqs.add(sb);
skipSeqs.add(se);
skipSeqs.add(skip);
skipSeqs.add("-");
// keep an augmented copy (for compose)
Compose.augment(0, g2pmodel, g2pmodel.getSemiring());
ArcSort.apply(g2pmodel, new ILabelCompare());
String[] isyms = g2pmodel.getIsyms();
loadClusters(isyms);
// get epsilon filter for composition
epsilonFilter = Compose.getFilter(g2pmodel.getIsyms(),
g2pmodel.getSemiring());
ArcSort.apply(epsilonFilter, new ILabelCompare());
}
/**
* Phoneticize a word
*
* @param entry
* the word to phoneticize transformed to an ArrayList of Strings
* (each element hold a single character)
* @param nbest
* the number of distinct pronunciations to return
* @return the pronunciation(s) of the input word
*/
public ArrayList<Path> phoneticize(ArrayList<String> entry, int nbest) {
Fst efst = entryToFSA(entry);
Semiring s = efst.getSemiring();
Compose.augment(1, efst, s);
ArcSort.apply(efst, new OLabelCompare());
Fst result = Compose.compose(efst, epsilonFilter, s, true);
ArcSort.apply(result, new OLabelCompare());
result = Compose.compose(result, g2pmodel, s, true);
Project.apply(result, ProjectType.OUTPUT);
if (nbest == 1) {
result = NShortestPaths.get(result, 1, false);
} else {
// Requesting 10 times more best paths than what was asking
// as there might be several paths resolving to same pronunciation
// due to epsilon transitions.
// I really hate cosmological constants :)
result = NShortestPaths.get(result, nbest * 10, false);
}
// result = NShortestPaths.get(result, nbest, false);
result = RmEpsilon.get(result);
ArrayList<Path> paths = findAllPaths(result, nbest, skipSeqs,
tie);
return paths;
}
/**
* Phoneticize a word
*
* @param word
* the word to phoneticize
* @param nbest
* the number of distinct pronunciations to return
* @return the pronunciation(s) of the input word
*/
public ArrayList<Path> phoneticize(String word, int nbest) {
ArrayList<String> entry = new ArrayList<String>(word.length());
for (int i = 0; i < word.length(); i++) {
String ch = word.substring(i, i + 1);
if (Utils.getIndex(g2pmodel.getIsyms(), ch) >= 0) {
entry.add(ch);
}
}
return phoneticize(entry, nbest);
}
/**
* Transforms an input spelling/pronunciation into an equivalent FSA, adding
* extra arcs as needed to accommodate clusters.
*
* @param entry
* the input vector
* @return the created fst
*/
private Fst entryToFSA(ArrayList<String> entry) {
TropicalSemiring ts = new TropicalSemiring();
Fst efst = new Fst(ts);
State s = new State(ts.zero());
efst.addState(s);
efst.setStart(s);
// Build the basic FSA
for (int i = 0; i < entry.size() + 1; i++) {
s = new State(ts.zero());
efst.addState(s);
if (i >= 1) {
int symIndex = Utils.getIndex(g2pmodel.getIsyms(),
entry.get(i - 1));
efst.getState(i).addArc(new Arc(symIndex, symIndex, 0.f, s));
} else if (i == 0) {
int symIndex = Utils.getIndex(g2pmodel.getIsyms(), sb);
efst.getStart().addArc(new Arc(symIndex, symIndex, 0.f, s));
}
if (i == entry.size()) {
State s1 = new State(ts.zero());
efst.addState(s1);
int symIndex = Utils.getIndex(g2pmodel.getIsyms(), se);
s.addArc(new Arc(symIndex, symIndex, 0.f, s1));
s1.setFinalWeight(0.f);
}
}
// Add any cluster arcs
for (int value = 0; value < clusters.length; value++) {
ArrayList<String> cluster = clusters[value];
if (cluster != null) {
int start = 0;
int k = 0;
while (k != -1) {
k = Utils.search(entry, cluster, start);
if (k != -1) {
State from = efst.getState(start + k + 1);
from.addArc(new Arc(value, value, 0.f, efst
.getState(start + k + cluster.size() + 1)));
start = start + k + cluster.size();
}
}
}
}
efst.setIsyms(g2pmodel.getIsyms());
efst.setOsyms(g2pmodel.getIsyms());
return efst;
}
/**
* Finds nbest paths in an Fst returned by NShortestPaths operation
*
* @param fst
* the input fst
* @param nbest
* the number of paths to return
* @param skipSeqs
* the sequences to ignore
* @param tie
* the separator symbol
* @return the paths
*/
@SuppressWarnings("unchecked")
private ArrayList<Path> findAllPaths(Fst fst, int nbest,
HashSet<String> skipSeqs, String tie) {
Semiring semiring = fst.getSemiring();
// ArrayList<Path> finalPaths = new ArrayList<Path>();
HashMap<String, Path> finalPaths = new HashMap<String, Path>();
HashMap<State, Path> paths = new HashMap<State, Path>();
Queue<State> queue = new LinkedList<State>();
Path p = new Path(fst.getSemiring());
p.setCost(semiring.one());
paths.put(fst.getStart(), p);
queue.add(fst.getStart());
String[] osyms = fst.getOsyms();
while (!queue.isEmpty()) {
State s = queue.remove();
Path currentPath = paths.get(s);
if (s.getFinalWeight() != semiring.zero()) {
String pathString = currentPath.getPath().toString();
if (finalPaths.containsKey(pathString)) {
// path already exist. update its cost
Path old = finalPaths.get(pathString);
if (old.getCost() > currentPath.getCost()) {
finalPaths.put(pathString, currentPath);
}
} else {
finalPaths.put(pathString, currentPath);
}
}
int numArcs = s.getNumArcs();
for (int j = 0; j < numArcs; j++) {
Arc a = s.getArc(j);
p = new Path(fst.getSemiring());
Path cur = paths.get(s);
p.setCost(cur.getCost());
p.setPath((ArrayList<String>) cur.getPath().clone());
String sym = osyms[a.getOlabel()];
String[] symsArray = sym.split("\\" + tie);
for (int i = 0; i < symsArray.length; i++) {
String phone = symsArray[i];
if (!skipSeqs.contains(phone)) {
p.getPath().add(phone);
}
}
p.setCost(semiring.times(p.getCost(), a.getWeight()));
State nextState = a.getNextState();
paths.put(nextState, p);
if (!queue.contains(nextState)) {
queue.add(nextState);
}
}
}
ArrayList<Path> res = new ArrayList<Path>();
for (Path path : finalPaths.values()) {
res.add(path);
}
Collections.sort(res, new PathComparator());
int numPaths = res.size();
for (int i = nbest; i < numPaths; i++) {
res.remove(res.size() - 1);
}
return res;
}
/**
* Initialize clusters
*/
@SuppressWarnings("unchecked")
private void loadClusters(String[] syms) {
clusters = new ArrayList[syms.length];
for (int i = 0; i < syms.length; i++) {
clusters[i] = null;
}
for (int i = 2; i < syms.length; i++) {
String sym = syms[i];
if (sym.contains(tie)) {
String split[] = sym.split(Pattern.quote(tie));
ArrayList<String> cluster = new ArrayList<String>(
Arrays.asList(split));
clusters[i] = cluster;
}
}
}
}