private Pair<Integer, Integer> updateTargetLimit(
Alignment a, int sourceStartIndex, int sourceEndIndex) {
Pair<Integer, Integer> res = new Pair<Integer, Integer>();
int minTargetIndex = a.getMinTargetIndex(sourceStartIndex);
int maxTargetIndex = a.getMaxTargetIndex(sourceStartIndex);
for (int sourceIndex = sourceStartIndex; sourceIndex <= sourceEndIndex; sourceIndex++) {
int minTargetIndexCandidate = a.getMinTargetIndex(sourceIndex);
int maxTargetIndexCandidate = a.getMaxTargetIndex(sourceIndex);
if (minTargetIndexCandidate < minTargetIndex) minTargetIndex = minTargetIndexCandidate;
if (maxTargetIndexCandidate > maxTargetIndex) maxTargetIndex = maxTargetIndexCandidate;
}
res.setFirst(minTargetIndex);
res.setSecond(maxTargetIndex);
return res;
}
/**
* This method extract phrase pairs from a Viterbi alignment and a sentence pair. Protected for
* testing.
*
* @param a
* @param sp
* @return
*/
private List<Rule> extractPhrasePairs(Alignment a, SentencePair sp) {
List<Rule> res = new ArrayList<Rule>();
// loop over source index (beginning of phrase)
for (int sourceStartIndex = 0;
sourceStartIndex < sp.getSource().getWords().length;
sourceStartIndex++) {
// source phrase built on the fly
List<Integer> sourcePhrase = new ArrayList<Integer>();
// maintain the minimum and maximum target index aligned to the
// source phrase
int minTargetIndex = a.getMinTargetIndex(sourceStartIndex);
int maxTargetIndex = a.getMaxTargetIndex(sourceStartIndex);
// loop over source index (end of phrase)
for (int sourceEndIndex = sourceStartIndex;
sourceEndIndex
< Math.min(sourceStartIndex + MAX_SOURCE_PHRASE, sp.getSource().getWords().length);
sourceEndIndex++) {
// update the sourcePhrase
sourcePhrase.add(sp.getSource().getWords()[sourceEndIndex]);
// update minimum and maximum target index aligned to the source
// phrase
int minTargetIndexCandidate = a.getMinTargetIndex(sourceEndIndex);
int maxTargetIndexCandidate = a.getMaxTargetIndex(sourceEndIndex);
if (minTargetIndexCandidate < minTargetIndex) minTargetIndex = minTargetIndexCandidate;
if (maxTargetIndexCandidate > maxTargetIndex) maxTargetIndex = maxTargetIndexCandidate;
if (minTargetIndex > maxTargetIndex) // occurs when haven't
// found any aligned
// word
// yet
continue;
// check if the target phrase between positions minTargetIndex
// and maxTargetIndex and the source phrase are consistent with
// the alignment
boolean consistent = true;
List<Integer> targetPhrase = new ArrayList<Integer>();
for (int targetIndex = minTargetIndex; targetIndex <= maxTargetIndex; targetIndex++) {
targetPhrase.add(sp.getTarget().getWords()[targetIndex]);
if (a.isTargetAligned(targetIndex)
&& (a.getMinSourceIndex(targetIndex) < sourceStartIndex
|| a.getMaxSourceIndex(targetIndex) > sourceEndIndex)) {
consistent = false;
break;
}
}
// we found a phrase pair
if (consistent) {
// TODO the rule may be constructed on the fly
// to avoid duplicated logic as well as duplicated loops.
Rule r =
new Rule(sourceStartIndex, sourceEndIndex, minTargetIndex, maxTargetIndex, sp, a);
res.add(r);
List<Rule> extendedUnaligned =
extendUnalignedBoundaryWord(
sourceStartIndex, sourceEndIndex, minTargetIndex, maxTargetIndex, a, sp);
res.addAll(extendedUnaligned);
}
}
}
return res;
}