filters.indexing.NegationScopeFilter.java Source code

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Here is the source code for filters.indexing.NegationScopeFilter.java

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// The MIT License
//
// Copyright (c) 2010 Stelios Karabasakis
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
package filters.indexing;

import indexing.PosTag;
import indexing.Token;
import java.io.IOException;
import java.util.logging.Level;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.FlagsAttribute;
import org.apache.lucene.analysis.tokenattributes.PayloadAttribute;
import org.apache.lucene.analysis.tokenattributes.TermAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.index.Payload;
import util.AppLogger;
import edu.stanford.nlp.util.ArrayUtils;

/**
 * TODO Description missing
 * @author Stelios Karabasakis
 */
public class NegationScopeFilter extends TokenFilter {

    public static String[] negationTerms = { "n't", "no", "not", "never", "none", "nothing", "nobody", "noone",
            "nowhere", "without", "hardly", "barely", "rarely", "seldom", "against", "minus", "off", "sans" };

    private boolean negative = false;

    private TermAttribute input_term;
    private TypeAttribute input_type;
    private FlagsAttribute input_flags;
    private PayloadAttribute input_payload;
    private TermAttribute output_term;
    private TypeAttribute output_type;
    private FlagsAttribute output_flags;
    private PayloadAttribute output_payload;

    /**
     * Constructor for class NegationScopeFilter
     * @param input
     */
    public NegationScopeFilter(TokenStream input) {
        super(input);

        // Getting attributes from input token stream
        input_term = input.getAttribute(TermAttribute.class);
        input_type = input.getAttribute(TypeAttribute.class);
        input_flags = input.getAttribute(FlagsAttribute.class);
        input_payload = input.getAttribute(PayloadAttribute.class);

        // Setting attributes for this token stream
        output_term = this.getAttribute(TermAttribute.class);
        output_type = this.getAttribute(TypeAttribute.class);
        output_flags = this.addAttribute(FlagsAttribute.class);
        output_payload = this.getAttribute(PayloadAttribute.class);

    }

    /* (non-Javadoc)
     * @see org.apache.lucene.analysis.TokenStream#incrementToken()
     */
    @Override
    public boolean incrementToken() throws IOException {
        // Load next token from input stream
        Token current_token;
        if ((current_token = getNextToken()) == null)
            return false;

        // If current token term belongs to the set of negation terms, switch the state of the
        // negation flag (i.e. prepare to mark the next open class term as negated). Or if this
        // is already the case, reverse the effect of the negation, to account for double negatives)
        if (ArrayUtils.contains(negationTerms, current_token.term)) {
            negative = !negative;
            return incrementToken();
        }

        // If we are within the scope of a negation, modify the token's payload accordingly and
        // reset the state of the negation flag
        if (negative) {
            if (current_token.isOpenClass()) {
                current_token.payload.setNegation(true);
                negative = false;
            }

            // If we reached the end of a phrase, reset the state of the negation flag
            else if (PosTag.isDelim(current_token.payload.getPosCat())) {
                negative = false;
            }
        }

        // Setting attributes for output stream
        output_term.setTermBuffer(current_token.term);
        output_type.setType(current_token.type);
        output_flags.setFlags(current_token.flags);
        output_payload.setPayload(current_token.payload.getPayload());

        return true;
    }

    private Token getNextToken() throws IOException {
        if (input.incrementToken()) {
            // Reading term attributes from input stream
            String term = input_term.term();
            String postag = input_type.type();
            int flags = input_flags.getFlags();
            Payload payload = input_payload.getPayload();

            // Adding token into buffer
            Token t = new Token(term, postag, flags);
            if (t.payload.decode(payload.getData()) == false) {
                AppLogger.error.log(Level.WARNING, "Invalid payload data for token [" + term + ":" + postag
                        + "] detected while reading input stream for NegationScopeFilter");
            }

            return t;
        } else
            return null;

    }
}