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/*
 *    Geotoolkit.org - An Open Source Java GIS Toolkit
 *    http://www.geotoolkit.org
 *
 *    (C) 2011-2012, Open Source Geospatial Foundation (OSGeo)
 *    (C) 2011-2012, Geomatys
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotoolkit.xml;


/**
 * A marker interface for empty XML elements. Note that an "nil" XML element may not be an
 * empty Java object, since the Java object can still be associated with {@link XLink} or
 * {@link NilReason} attributes. Those attributes are not part of ISO 19115, but may appear
 * in ISO 19139 XML documents like below:
 *
 * 
 *   
 *   
 * Non-empty Series element Empty Series element

 * {@preformat xml
 *   
 *     
 *       
 *         
 *       
 *     
 *   
 * }
 * 
 * {@preformat xml
 *   
 *     
 *   
 * }
 * 
 *
 * The reason why an object is empty can be obtained by the {@link #getNilReason()} method.
 *
 * {@section Instantiation}
 * The following example instantiates a {@link org.opengis.metadata.citation.Citation} object
 * which is empty because the information are missing:
 *
 * {@preformat java
 *     Citation nil = NilReason.MISSING.createNilObject(Citation.class);
 * }
 *
 * @author Martin Desruisseaux (Geomatys)
 * @version 3.18
 *
 * @see NilReason#createNilObject(Class)
 * @see ObjectLinker#resolve(Class, NilReason)
 *
 * @since 3.18
 * @module
 */
public interface NilObject {
    /**
     * Returns the reason why this object is empty.
     *
     * @return The reason why this object is empty.
     */
    NilReason getNilReason();
}