de.up.ling.irtg.maxent

Class FeatureFunction<State,V>

java.lang.Object

de.up.ling.irtg.maxent.FeatureFunction<State,V>

Direct Known Subclasses:

ChildOfFeature, RuleNameFeature

public abstract class FeatureFunction<State,V>
extends Object

A feature function for a log-linear model that assigns a value to a chart rule. Technically, the value is assigned by executing the evaluate(de.up.ling.irtg.automata.Rule, de.up.ling.irtg.automata.TreeAutomaton, de.up.ling.irtg.maxent.MaximumEntropyIrtg, java.util.Map) method on each rule of a TreeAutomaton with state set State. The evaluate method can additionally see the Rule itself, the MaximumEntropyIrtg from which the rule originally came, and the inputs that are being parsed.

For instance, in a log-linear model for a context-free grammar, you will have a MaximumEntropyIrtg with a single interpretation into the StringAlgebra. Therefore the states of the chart will be pairs of String (= nonterminal from the grammar) and StringAlgebra.Span (indicating a span in the input string). A feature function will be passed the rule in the chart; the chart itself; the IRTG grammar; and a map that maps the interpretation name to the string that is currently being parsed. A feature that responds to the first and last words in the span can look these up in the string.

Concrete implementations of FeatureFunction must implement the evaluate(de.up.ling.irtg.automata.Rule, de.up.ling.irtg.automata.TreeAutomaton, de.up.ling.irtg.maxent.MaximumEntropyIrtg, java.util.Map) method. Note that feature values can come from any class V, but the standard methods for training and parsing in MaximumEntropyIrtg only support V = Double.

Author:

koller

Constructor Summary

Constructors

Constructor and Description
FeatureFunction()

Method Summary

Modifier and Type	Method and Description
abstract V	evaluate(Rule rule, TreeAutomaton<State> automaton, MaximumEntropyIrtg irtg, Map<String,Object> inputs) Computes the value of the feature function for a given rule.
String	toString()

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

FeatureFunction

public FeatureFunction()

Method Detail

evaluate

public abstract V evaluate(Rule rule,
                           TreeAutomaton<State> automaton,
                           MaximumEntropyIrtg irtg,
                           Map<String,Object> inputs)

Computes the value of the feature function for a given rule. Implement this method in a subclass to realize the actual feature function.

Parameters:

rule - a rule in "automaton"

automaton - the tree automaton to which "rule" belongs, typically a parse chart

irtg - the maxent IRTG which defined the grammar rule on which "rule" is based

inputs - the inputs that are currently being parsed

Returns:

the value of this feature function on those inputs

toString

public String toString()

Overrides:

toString in class Object