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 * Redistribution and use of this software and associated documentation ("Software"), with or
 * without modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright statements and notices. Redistributions
 * must also contain a copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided with
 * the distribution.
 *
 * 3. The name "Exolab" must not be used to endorse or promote products derived from this Software
 * without prior written permission of Intalio, Inc. For written permission, please contact
 * info@exolab.org.
 *
 * 4. Products derived from this Software may not be called "Exolab" nor may "Exolab" appear in
 * their names without prior written permission of Intalio, Inc. Exolab is a registered trademark of
 * Intalio, Inc.
 *
 * 5. Due credit should be given to the Exolab Project (http://www.exolab.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY INTALIO, INC. AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESSED OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL INTALIO, INC. OR ITS
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 1999-2000 (C) Intalio, Inc. All Rights Reserved.
 *
 */

package org.exolab.castor.xml.schema;

/**
 * Defines an object resolver but does not specify any implementation.
 * <p>
 * A lazy resolver would resolve an object given its identifier. The reference to the object will be
 * created with a {@link ResolvableReference} object using the resolved and the identifier. When the
 * object is requested, the {@link #resolve} method will be called to obtain it.
 * <p>
 * Some implementation will add and remove resolvable objects, e.g. a collection of objects that
 * also acts as a resolver. These methods should implement {@link #addResolvable} and
 * {@link #removeResolvable}. Resolvers that do not implement these methods are still considered
 * valid resolvers. For example, a database based resolver will operate consistently without
 * implementing add/remove not through the database interface.
 *
 * @author <a href="arkin@intalio.com">Assaf Arkin</a>
 * @see ResolvableReference
 **/
public interface Resolver {


  /**
   * Called to resolve a reference give the reference's identifier. If the reference is known, this
   * method should return the referenced object. If the reference is unknown, this method should
   * return null.
   *
   * @param id The identifier to resolve
   * @return The resolved object
   **/
  public Referable resolve(String id);


  /**
   * Adds a resolvable object to this resolver identified by <tt>id</tt>. Subsequent calls to
   * {@link #resolve} with the same <tt>id</tt> will return <tt>referent</tt>.
   *
   * @param id The referent's identifier
   * @param referent The referent object
   */
  public void addResolvable(String id, Referable referent);


  /**
   * Removes a resolvable object from this resolver. Subsequent calls to {@link #resolve} with the
   * same <tt>id</tt> will return null.
   *
   * @param id The referent's identifier
   */
  public void removeResolvable(String id);


}

