XLingDocModel.hpp

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/*==========================================================================
 * Copyright (c) 2004 University of Massachusetts.  All Rights Reserved.
 *
 * Use of the Lemur Toolkit for Language Modeling and Information Retrieval
 * is subject to the terms of the software license set forth in the LICENSE
 * file included with this software, and also available at
 * http://www.lemurproject.org/license.html
 *
 *==========================================================================
 */


#ifndef _XLINGDOCMODEL_HPP
#define _XLINGDOCMODEL_HPP

#include "RetrievalMethod.hpp"
#include "Index.hpp"
#include "DocumentRep.hpp"

namespace lemur 
{
  namespace retrieval 
  {
    
    class XLingDocModel : public lemur::api::DocumentRep {
    public:
      XLingDocModel(lemur::api::DOCID_T docID, const lemur::api::Index *ind, 
                    double l, double nt, bool sM = false) :
        lemur::api::DocumentRep(docID, ind->docLength(docID)), refIndex(ind), lambda(l), 
        numTerms(nt),  docBasedSmooth(sM) {
      };
  
      ~XLingDocModel() {};
      virtual double termWeight(lemur::api::TERMID_T termID, const lemur::api::DocInfo *info) const {
        //    double p_doc = info->termCount()/(double)refIndex->docLength(id);
        double p_doc = info->termCount()/(double)docLength;
        double p_gen; 
        if (docBasedSmooth) 
          p_gen = refIndex->docCount(termID)/numTerms;
        else 
          p_gen = refIndex->termCount(termID)/numTerms;
        return ((lambda * p_doc) + ((1 - lambda) * p_gen));
      }

      virtual double scoreConstant() const {
        return lambda;
      }

    protected:
      const lemur::api::Index *refIndex;
      double numTerms;
      double lambda;
      bool docBasedSmooth;
    };
  }
}

#endif /* _XLINGDOCMODEL_HPP */

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