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/**
 * 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 org.apache.mahout.cf.taste.model;

import java.io.Serializable;

import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.common.LongPrimitiveIterator;

/**
 * 

* Implementations represent a repository of information about users and their associated {@link Preference}s * for items. *

*/ public interface DataModel extends Refreshable, Serializable { /** * @return all user IDs in the model, in order * @throws TasteException * if an error occurs while accessing the data */ LongPrimitiveIterator getUserIDs() throws TasteException; /** * @param userID * ID of user to get prefs for * @return user's preferences, ordered by item ID * @throws org.apache.mahout.cf.taste.common.NoSuchUserException * if the user does not exist * @throws TasteException * if an error occurs while accessing the data */ PreferenceArray getPreferencesFromUser(long userID) throws TasteException; /** * @param userID * ID of user to get prefs for * @return IDs of items user expresses a preference for * @throws org.apache.mahout.cf.taste.common.NoSuchUserException * if the user does not exist * @throws TasteException * if an error occurs while accessing the data */ FastIDSet getItemIDsFromUser(long userID) throws TasteException; /** * @return a {@link LongPrimitiveIterator} of all item IDs in the model, in order * @throws TasteException * if an error occurs while accessing the data */ LongPrimitiveIterator getItemIDs() throws TasteException; /** * @param itemID * item ID * @return all existing {@link Preference}s expressed for that item, ordered by user ID, as an array * @throws org.apache.mahout.cf.taste.common.NoSuchItemException * if the item does not exist * @throws TasteException * if an error occurs while accessing the data */ PreferenceArray getPreferencesForItem(long itemID) throws TasteException; /** * Retrieves the preference value for a single user and item. * * @param userID * user ID to get pref value from * @param itemID * item ID to get pref value for * @return preference value from the given user for the given item or null if none exists * @throws org.apache.mahout.cf.taste.common.NoSuchUserException * if the user does not exist * @throws TasteException * if an error occurs while accessing the data */ Float getPreferenceValue(long userID, long itemID) throws TasteException; /** * Retrieves the time at which a preference value from a user and item was set, if known. * Time is expressed in the usual way, as a number of milliseconds since the epoch. * * @param userID user ID for preference in question * @param itemID item ID for preference in question * @return time at which preference was set or null if no preference exists or its time is not known * @throws org.apache.mahout.cf.taste.common.NoSuchUserException if the user does not exist * @throws TasteException if an error occurs while accessing the data */ Long getPreferenceTime(long userID, long itemID) throws TasteException; /** * @return total number of items known to the model. This is generally the union of all items preferred by * at least one user but could include more. * @throws TasteException * if an error occurs while accessing the data */ int getNumItems() throws TasteException; /** * @return total number of users known to the model. * @throws TasteException * if an error occurs while accessing the data */ int getNumUsers() throws TasteException; /** * @param itemID item ID to check for * @return the number of users who have expressed a preference for the item * @throws TasteException if an error occurs while accessing the data */ int getNumUsersWithPreferenceFor(long itemID) throws TasteException; /** * @param itemID1 first item ID to check for * @param itemID2 second item ID to check for * @return the number of users who have expressed a preference for the items * @throws TasteException if an error occurs while accessing the data */ int getNumUsersWithPreferenceFor(long itemID1, long itemID2) throws TasteException; /** *

* Sets a particular preference (item plus rating) for a user. *

* * @param userID * user to set preference for * @param itemID * item to set preference for * @param value * preference value * @throws org.apache.mahout.cf.taste.common.NoSuchItemException * if the item does not exist * @throws org.apache.mahout.cf.taste.common.NoSuchUserException * if the user does not exist * @throws TasteException * if an error occurs while accessing the data */ void setPreference(long userID, long itemID, float value) throws TasteException; /** *

* Removes a particular preference for a user. *

* * @param userID * user from which to remove preference * @param itemID * item to remove preference for * @throws org.apache.mahout.cf.taste.common.NoSuchItemException * if the item does not exist * @throws org.apache.mahout.cf.taste.common.NoSuchUserException * if the user does not exist * @throws TasteException * if an error occurs while accessing the data */ void removePreference(long userID, long itemID) throws TasteException; /** * @return true if this implementation actually stores and returns distinct preference values; * that is, if it is not a 'boolean' DataModel */ boolean hasPreferenceValues(); /** * @return the maximum preference value that is possible in the current problem domain being evaluated. For * example, if the domain is movie ratings on a scale of 1 to 5, this should be 5. While a * {@link org.apache.mahout.cf.taste.recommender.Recommender} may estimate a preference value above 5.0, it * isn't "fair" to consider that the system is actually suggesting an impossible rating of, say, 5.4 stars. * In practice the application would cap this estimate to 5.0. Since evaluators evaluate * the difference between estimated and actual value, this at least prevents this effect from unfairly * penalizing a {@link org.apache.mahout.cf.taste.recommender.Recommender} */ float getMaxPreference(); /** * @see #getMaxPreference() */ float getMinPreference(); }




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