/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 opennlp.tools.languagemodel;

import opennlp.tools.util.StringList;

/**
 * A language model can calculate the probability <i>p</i> (between 0 and 1) of a
 * certain {@link opennlp.tools.util.StringList sequence of tokens}, given its underlying vocabulary.
 */
public interface LanguageModel {

  /**
   * Calculate the probability of a series of tokens (e.g. a sentence), given a vocabulary
   *
   * @param tokens the text tokens to calculate the probability for
   * @return the probability of the given text tokens in the vocabulary
   */
  double calculateProbability(StringList tokens);

  /**
   * Predict the most probable output sequence of tokens, given an input sequence of tokens
   *
   * @param tokens a sequence of tokens
   * @return the most probable subsequent token sequence
   */
  StringList predictNextTokens(StringList tokens);

}