QuestionKeywordsFilter.java

package info.ephyra.answerselection.filters;

import info.ephyra.questionanalysis.KeywordExtractor;
import info.ephyra.search.Result;

/**
 * <p>A filter that drops a result if the answer string contains a keyword from
 * the question. Useful to eliminate answers that simply repeat the question,
 * e.g. without this filter a likely answer to the question "Who killed JFK?"
 * would be "JFK".</p>
 * 
 * <p>Note that this filter causes problems if a correct answer repeats part of
 * the question, e.g. answers to the question "What are the members of the
 * Kennedy clan?" also contain the keyword "Kennedy".</p>
 * 
 * <p>This class extends the class <code>Filter</code>.</p>
 * 
 * @author Nico Schlaefer
 * @version 2007-04-16
 */
public class QuestionKeywordsFilter extends Filter {
	/**
	 * Filters a single <code>Result</code> object.
	 * 
	 * @param result result to filter
	 * @return result or <code>null</code>
	 */
	public Result apply(Result result) {
		String[] tokens = KeywordExtractor.tokenize(result.getAnswer());
		String[] kws = result.getQuery().getAnalyzedQuestion().getKeywords();
		for (String token : tokens)
			for (String kw : kws)
				if (token.equalsIgnoreCase(kw)) return null;
		
		return result;
	}
}