package edu.northwestern.at.utils.corpuslinguistics.postagger.simplerulebased;
/* Please see the license information at the end of this file. */
import java.util.*;
import edu.northwestern.at.utils.*;
import edu.northwestern.at.utils.corpuslinguistics.adornedword.*;
import edu.northwestern.at.utils.corpuslinguistics.partsofspeech.*;
import edu.northwestern.at.utils.corpuslinguistics.postagger.*;
import edu.northwestern.at.utils.corpuslinguistics.postagger.unigram.*;
import edu.northwestern.at.utils.corpuslinguistics.tokenizer.*;
/** Simple Rule-Based Part of Speech tagger.
*
* <p>
* The simple rule-based part of speech tagger assigns the most
* commonly occurring part of speech to all words and then
* applies a small set of contextual rules to "fix up" the tagging.
* It's kind of a "Brill light."
* </p>
*
* <p>
* This simple tagger is useful when very fast tagging without
* high accuracy is useful, e.g., in sentence splitting.
* </p>
*/
public class SimpleRuleBasedTagger
extends UnigramTagger
implements PartOfSpeechTagger, PartOfSpeechRetagger
{
/** Create a simple rule-based tagger.
*/
public SimpleRuleBasedTagger()
{
}
/** Tag a sentence.
*
* @param sentence The sentence as a list of string words.
*
* @return An {@link edu.northwestern.at.utils.corpuslinguistics.adornedword.AdornedWord}
* of the words in the sentence tagged with
* parts of speech.
*
* <p>
* The input sentence is a {@link java.util.List} of
* string words to be tagged. The output is
* {@link edu.northwestern.at.utils.corpuslinguistics.adornedword.AdornedWord}
* of the words with parts of speech added.
* </p>
*/
public List<AdornedWord> tagSentence( List<String> sentence )
{
// Get unigram tagger results.
// This assigns the most common tag
// to each word.
List<AdornedWord> taggedSentence = super.tagSentence( sentence );
// Apply the fixup rules.
return retagWords( taggedSentence );
}
/** Retag words in a tagged sentence.
*
* @param taggedSentence The tagged sentence.
*
* @return The retagged sentence.
*
* <p>
* This method applies the short list of fixup rules.
* The resultant tagging is crude but good enough
* for tasks like sentence boundary detection.
* </p>
*/
public<T extends AdornedWord> List<T> retagWords
(
List<T> taggedSentence
)
{
// Get part of speech tags used
// for tagging this sentence.
PartOfSpeechTags posTags = lexicon.getPartOfSpeechTags();
// Previous word in sentence.
T previousWord = null;
// Loop over words in sentence.
for ( int i = 0 ; i < taggedSentence.size() ; i++ )
{
// Get current word in sentence.
T word = taggedSentence.get( i );
// Get spelling and parts of speech
// for word.
String spelling = word.getSpelling();
String posTag = word.getPartsOfSpeech();
// Rule 1:
// determiner followed by
// verb -> determiner followed
// by noun.
if ( previousWord != null )
{
if ( posTags.isDeterminerTag(
previousWord.getPartsOfSpeech() ) &&
posTags.isVerbTag( posTag )
)
{
word.setPartsOfSpeech( posTags.getSingularNounTag() );
}
}
// Rule 2: convert a noun to a
// past participle if word ends with "ed"
if ( ( posTags.isNounTag( posTag ) &&
!posTags.isProperNounTag( posTag )
) && spelling.endsWith( "ed" )
)
{
word.setPartsOfSpeech( posTags.getPastParticipleTag() );
}
// Rule 3: convert any type to adverb
// if it ends in "ly".
if ( spelling.endsWith( "ly" ) )
{
word.setPartsOfSpeech( posTags.getAdverbTag() );
}
// Rule 4: convert a common noun to an
// adjective if it ends with "al".
if ( ( posTags.isNounTag( posTag ) &&
!posTags.isProperNounTag( posTag )
) && spelling.endsWith( "al" )
)
{
word.setPartsOfSpeech( posTags.getAdjectiveTag() );
}
// Rule 5: convert a noun to a verb
// if the preceeding word is "would".
if ( previousWord != null )
{
if ( ( posTags.isNounTag( posTag ) &&
!posTags.isProperNounTag( posTag )
) &&
previousWord.getSpelling().equalsIgnoreCase( "would" )
)
{
word.setPartsOfSpeech( posTags.getVerbTag() );
}
}
// Rule 6: if a word has been categorized
// as a common noun and it ends with "s",
// set its part of speech to plural
// common noun.
if ( posTag.equals( posTags.getSingularNounTag() ) &&
spelling.endsWith( "s" )
)
{
word.setPartsOfSpeech( posTags.getPluralNounTag() );
}
// Rule 7: convert a common noun to a
// present participle verb.
if ( spelling.endsWith( "ing" ) )
{
if ( posTags.isNounTag( posTag ) &&
!posTags.isProperNounTag( posTag )
)
{
word.setPartsOfSpeech(
posTags.getPresentParticipleTag() );
}
}
// Set previous word to current word.
previousWord = word;
// Replace word with updated word.
taggedSentence.remove( i );
taggedSentence.add( i , word );
}
return taggedSentence;
}
/** Retag a sentence.
*
* @param sentence The sentence as an
* {@link edu.northwestern.at.utils.corpuslinguistics.adornedword.AdornedWord} .
*
* @return The sentence with words retagged.
*/
public<T extends AdornedWord> List<T> retagSentence
(
List<T> sentence
)
{
return retagWords( sentence );
}
/** Can retagger add or delete words in the original sentence?
*
* @return true if retagger can add or delete words.
*/
public boolean canAddOrDeleteWords()
{
return true;
}
/** Return tagger description.
*
* @return Tagger description.
*/
public String toString()
{
return "Simple rule based tagger";
}
}
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