code: /*
   * Copyright 2015 recommenders.net.
   *
   * 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 net.recommenders.rival.core;
  
  /**
   * Interface for the data model used throughout the toolkit. Able to store
   * users, items, and preferences.
   *
   * @author <a href="http://github.com/abellogin">Alejandro</a>, <a
   * href="http://github.com/alansaid">Alan</a>
   *
   * @param <U> generic type for users
   * @param <I> generic type for items
   */
  public interface DataModelIF<U, I> {
  
      /**
       * Method that returns the preference between a user and an item.
       *
       * @param u the user.
       * @param i the item.
       * @return the preference between a user and an item.
       */
      public Double getUserItemPreference(U u, I i);
  
      /**
       * Method that returns the items of a user.
       *
       * @param u the user.
       * @return the items of a user.
       */
      public Iterable<I> getUserItems(U u);
  
      /**
       * Method that adds a preference to the model between a user and an item.
       *
       * @param u the user.
       * @param i the item.
       * @param d the preference.
       */
      public void addPreference(final U u, final I i, final Double d);
  
      /**
       * Method that returns the items in the model.
       *
       * @return the items in the model.
       */
      public Iterable<I> getItems();
  
      /**
       * Method that returns the users in the model.
       *
       * @return the users in the model.
       */
      public Iterable<U> getUsers();
  
      /**
       * Method that returns the number of items in the model.
       *
       * @return the number of items in the model.
       */
      public int getNumItems();
  
      /**
       * Method that returns the number of users in the model.
       *
       * @return the number of users in the model.
       */
      public int getNumUsers();
  
      /**
       * Method that clears all the maps contained in the model.
       */
      public void clear();
  }
  