/*
 * Ivory: A Hadoop toolkit for Web-scale information retrieval
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you
 * may not use this file except in compliance with the License. You may
 * obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0 
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package ivory.lsh.data;

/**
 * <p>
 * Interface to object that keeps track of the document frequency of each term
 * in the collection. Concrete classes may vary in terms of implementation,
 * e.g., hashes (faster lookup, but less memory efficient) or arrays (slower
 * binary search lookup, but more memory efficient).
 * </p>
 * 
 * @author Jimmy Lin
 * 
 */
public interface DfTable {

  /**
   * Returns the document frequency of a term.
   */
  public int getDf(String term);

  /**
   * Returns the number of documents in the collection.
   */
  public int getDocumentCount();

  /**
   * Returns the number of unique terms in the collection.
   */
  public int getVocabularySize();

  /**
   * Returns the document frequency of the term with the highest document
   * frequency.
   */
  public int getMaxDf();

  /**
   * Returns the term with the highest document frequency.
   */
  public String getMaxDfTerm();

  /**
   * Returns the number of terms that only appear in one document.
   */
  public int getCountOfTermWithDfOne();
}