/**
* Builds a Trellis over a sentence, by starting at the state State, and advancing through all
* legal extensions of each state already in the trellis. You should not have to modify this
* code (or even read it, really).
*/
private Trellis<State> buildTrellis(List<String> sentence) {
Trellis<State> trellis = new Trellis<State>();
trellis.setStartState(State.getStartState());
State stopState = State.getStopState(sentence.size() + 2);
trellis.setStopState(stopState);
Set<State> states = Collections.singleton(State.getStartState());
for (int position = 0; position <= sentence.size() + 1; position++) {
Set<State> nextStates = new HashSet<State>();
for (State state : states) {
if (state.equals(stopState)) continue;
LocalTrigramContext localTrigramContext =
new LocalTrigramContext(
sentence, position, state.getPreviousPreviousTag(), state.getPreviousTag());
Counter<String> tagScores = localTrigramScorer.getLogScoreCounter(localTrigramContext);
for (String tag : tagScores.keySet()) {
double score = tagScores.getCount(tag);
State nextState = state.getNextState(tag);
trellis.setTransitionCount(state, nextState, score);
nextStates.add(nextState);
}
}
// System.out.println("States: "+nextStates);
states = nextStates;
}
return trellis;
}
/**
* Scores a tagging for a sentence. Note that a tag sequence not accepted by the markov process
* should receive a log score of Double.NEGATIVE_INFINITY.
*/
public double scoreTagging(TaggedSentence taggedSentence) {
double logScore = 0.0;
List<LabeledLocalTrigramContext> labeledLocalTrigramContexts =
extractLabeledLocalTrigramContexts(taggedSentence);
for (LabeledLocalTrigramContext labeledLocalTrigramContext : labeledLocalTrigramContexts) {
Counter<String> logScoreCounter =
localTrigramScorer.getLogScoreCounter(labeledLocalTrigramContext);
String currentTag = labeledLocalTrigramContext.getCurrentTag();
if (logScoreCounter.containsKey(currentTag)) {
logScore += logScoreCounter.getCount(currentTag);
} else {
logScore += Double.NEGATIVE_INFINITY;
}
}
return logScore;
}
// chop up the validation instances into local contexts and pass them on to the local scorer.
public void validate(List<TaggedSentence> taggedSentences) {
localTrigramScorer.validate(extractLabeledLocalTrigramContexts(taggedSentences));
}
// chop up the training instances into local contexts and pass them on to the local scorer.
public void train(List<TaggedSentence> taggedSentences) {
localTrigramScorer.train(extractLabeledLocalTrigramContexts(taggedSentences));
}
