/** Updates the agenda with of any unary rules that can be applied. */
private void updateAgendaUnary(
final Model model, final AgendaItem newItem, final PriorityQueue<AgendaItem> agenda) {
final SyntaxTreeNode parse = newItem.getParse();
final List<UnaryRule> ruleProductions = unaryRules.get(parse.getCategory());
final int size = ruleProductions.size();
if (size == 0) {
return;
}
final boolean isNotPunctuationNode =
parse.getRuleType() != RuleType.LP && parse.getRuleType() != RuleType.RP;
for (int i = 0; i < size; i++) {
final UnaryRule unaryRule = ruleProductions.get(i);
if (isNotPunctuationNode || unaryRule.isTypeRaising()) {
// Don't allow unary rules to apply to the output of non-type-raising rules.
// i.e. don't allow both (NP (N ,))
// The reason for allowing type-raising is to simplify Eisner Normal Form contraints (a
// punctuation rule would mask the fact that a rule is the output of type-raising).
// TODO should probably refactor the constraint into NormalForm.
SyntaxTreeNodeUnary newNode;
if (usingDependencies) {
final List<UnlabelledDependency> resolvedDependencies = new ArrayList<>();
newNode =
new SyntaxTreeNodeUnary(
unaryRule.getResult(),
parse,
unaryRule
.getDependencyStructureTransformation()
.apply(parse.getDependencyStructure(), resolvedDependencies),
unaryRule,
resolvedDependencies);
} else {
newNode = new SyntaxTreeNodeUnary(unaryRule.getResult(), parse, null, unaryRule, null);
}
agenda.add(model.unary(newItem, newNode, unaryRule));
}
}
}
@Override
protected List<Scored<SyntaxTreeNode>> parse(final InputToParser input) {
ChartCellFactory sentenceCellFactory = cellFactory.forNewSentence();
final List<InputWord> sentence = input.getInputWords();
final Model model = modelFactory.make(input);
final int sentenceLength = sentence.size();
final PriorityQueue<AgendaItem> agenda = new PriorityQueue<>(1000);
model.buildAgenda(agenda, sentence);
final ChartCell[][] chart = new ChartCell[sentenceLength][sentenceLength];
final List<Scored<SyntaxTreeNode>> result = new ArrayList<>(nbest);
int chartSize = 0;
// Track which cells in the chart are non-empty. This is helpful, because the A* chart is very
// sparse compared
// to CKY charts.
final List<List<ChartCell>> cellsStartingAt = new ArrayList<>(sentenceLength + 1);
final List<List<ChartCell>> cellsEndingAt = new ArrayList<>(sentenceLength + 1);
for (int i = 0; i < sentenceLength + 1; i++) {
cellsStartingAt.add(new ArrayList<>());
cellsEndingAt.add(new ArrayList<>());
}
// Dummy final cell that the complete parses are stored in.
final ChartCell finalCell = sentenceCellFactory.make();
while (chartSize < maxChartSize
&& (result.isEmpty()
|| (result.size() < nbest
&& !agenda.isEmpty()
&& agenda.peek().getCost() > nbestBeam * result.get(0).getScore()))) {
// Add items from the agenda, until we have enough parses.
final AgendaItem agendaItem = agenda.poll();
if (agendaItem == null) {
break;
}
// Try to put an entry in the chart.
ChartCell cell = chart[agendaItem.getStartOfSpan()][agendaItem.getSpanLength() - 1];
if (cell == null) {
cell = sentenceCellFactory.make();
chart[agendaItem.getStartOfSpan()][agendaItem.getSpanLength() - 1] = cell;
cellsStartingAt.get(agendaItem.getStartOfSpan()).add(cell);
cellsEndingAt.get(agendaItem.getStartOfSpan() + agendaItem.getSpanLength()).add(cell);
}
if (cell.add(agendaItem)) {
chartSize++;
// If a new entry was added, update the agenda.
// Is the new entry an acceptable complete parse?
if (agendaItem.getSpanLength() == sentenceLength
&& agendaItem.getInsideScore() > Double.NEGATIVE_INFINITY
&& (possibleRootCategories.isEmpty()
|| possibleRootCategories.contains(agendaItem.getParse().getCategory()))
&&
// For N-best parsing, the final cell checks if that the final parse is unique. e.g. if
// it's
// dependencies are unique, ignoring the category
finalCell.add("", agendaItem)) {
result.add(new Scored<>(agendaItem.getParse(), agendaItem.getInsideScore()));
}
// See if any Unary Rules can be applied to the new entry.
updateAgendaUnary(model, agendaItem, agenda);
// See if the new entry can be the left argument of any binary rules.
for (final ChartCell rightCell :
cellsStartingAt.get(agendaItem.getStartOfSpan() + agendaItem.getSpanLength())) {
for (final AgendaItem rightEntry : rightCell.getEntries()) {
updateAgenda(agenda, agendaItem, rightEntry, model);
}
}
// See if the new entry can be the right argument of any binary
// rules.
for (final ChartCell leftCell : cellsEndingAt.get(agendaItem.getStartOfSpan())) {
for (final AgendaItem leftEntry : leftCell.getEntries()) {
updateAgenda(agenda, leftEntry, agendaItem, model);
}
}
}
}
if (result.size() == 0) {
// Parse failure.
return null;
}
return result;
}
/**
* Updates the agenda with the result of all combinators that can be applied to leftChild and
* rightChild.
*/
private void updateAgenda(
final PriorityQueue<AgendaItem> agenda,
final AgendaItem left,
final AgendaItem right,
final Model model) {
final SyntaxTreeNode leftChild = left.getParse();
final SyntaxTreeNode rightChild = right.getParse();
if (!seenRules.isSeen(leftChild.getCategory(), rightChild.getCategory())) {
return;
}
final List<RuleProduction> rules = getRules(leftChild.getCategory(), rightChild.getCategory());
final int size = rules.size();
for (int i = 0; i < size; i++) {
final RuleProduction production = rules.get(i);
// Check if normal-form constraints let us add this rule.
if (NormalForm.isOk(
leftChild.getRuleClass(),
rightChild.getRuleClass(),
production.getRuleType(),
leftChild.getCategory(),
rightChild.getCategory(),
production.getCategory(),
left.getStartOfSpan() == 0)) {
final SyntaxTreeNodeBinary newNode;
if (usingDependencies) {
// Update all the information for tracking dependencies.
final List<UnlabelledDependency> resolvedDependencies = new ArrayList<>();
final DependencyStructure newDependencies =
production
.getCombinator()
.apply(
leftChild.getDependencyStructure(),
rightChild.getDependencyStructure(),
resolvedDependencies);
final boolean headIsLeft =
newDependencies.getArbitraryHead()
== leftChild.getDependencyStructure().getArbitraryHead();
newNode =
new SyntaxTreeNodeBinary(
production.getCategory(),
leftChild,
rightChild,
production.getRuleType(),
headIsLeft,
newDependencies,
resolvedDependencies);
} else {
// If we're not modeling dependencies, we can save a lot of work.
newNode =
new SyntaxTreeNodeBinary(
production.getCategory(),
leftChild,
rightChild,
production.getRuleType(),
production.isHeadIsLeft(),
null,
null);
}
agenda.add(model.combineNodes(left, right, newNode));
}
}
}