org.codelibs.elasticsearch.taste.model.IDMigrator Maven / Gradle / Ivy
/**
* 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.codelibs.elasticsearch.taste.model;
import org.codelibs.elasticsearch.taste.common.Refreshable;
/**
*
* Mahout 0.2 changed the framework to operate only in terms of numeric (long) ID values for users and items.
* This is, obviously, not compatible with applications that used other key types -- most commonly
* {@link String}. Implementation of this class provide support for mapping String to longs and vice versa in
* order to provide a smoother migration path to applications that must still use strings as IDs.
*
*
*
* The mapping from strings to 64-bit numeric values is fixed here, to provide a standard implementation that
* is 'portable' or reproducible outside the framework easily. See {@link #toLongID(String)}.
*
*
*
* Because this mapping is deterministically computable, it does not need to be stored. Indeed, subclasses'
* job is to store the reverse mapping. There are an infinite number of strings but only a fixed number of
* longs, so, it is possible for two strings to map to the same value. Subclasses do not treat this as an
* error but rather retain only the most recent mapping, overwriting a previous mapping. The probability of
* collision in a 64-bit space is quite small, but not zero. However, in the context of a collaborative
* filtering problem, the consequence of a collision is small, at worst -- perhaps one user receives another
* recommendations.
*
*
* @since 0.2
*/
public interface IDMigrator extends Refreshable {
/**
* @return the top 8 bytes of the MD5 hash of the bytes of the given {@link String}'s UTF-8 encoding as a
* long.
*/
long toLongID(String stringID);
/**
* @return the string ID most recently associated with the given long ID, or null if doesn't exist
*/
String toStringID(long longID);
}