001    /*
002     *    GeoAPI - Java interfaces for OGC/ISO standards
003     *    http://www.geoapi.org
004     *
005     *    Copyright (C) 2006-2012 Open Geospatial Consortium, Inc.
006     *    All Rights Reserved. http://www.opengeospatial.org/ogc/legal
007     *
008     *    Permission to use, copy, and modify this software and its documentation, with
009     *    or without modification, for any purpose and without fee or royalty is hereby
010     *    granted, provided that you include the following on ALL copies of the software
011     *    and documentation or portions thereof, including modifications, that you make:
012     *
013     *    1. The full text of this NOTICE in a location viewable to users of the
014     *       redistributed or derivative work.
015     *    2. Notice of any changes or modifications to the OGC files, including the
016     *       date changes were made.
017     *
018     *    THIS SOFTWARE AND DOCUMENTATION IS PROVIDED "AS IS," AND COPYRIGHT HOLDERS MAKE
019     *    NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
020     *    TO, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT
021     *    THE USE OF THE SOFTWARE OR DOCUMENTATION WILL NOT INFRINGE ANY THIRD PARTY
022     *    PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS.
023     *
024     *    COPYRIGHT HOLDERS WILL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL OR
025     *    CONSEQUENTIAL DAMAGES ARISING OUT OF ANY USE OF THE SOFTWARE OR DOCUMENTATION.
026     *
027     *    The name and trademarks of copyright holders may NOT be used in advertising or
028     *    publicity pertaining to the software without specific, written prior permission.
029     *    Title to copyright in this software and any associated documentation will at all
030     *    times remain with copyright holders.
031     */
032    package org.opengis.filter;
033    
034    // OpenGIS direct dependencies
035    import org.opengis.annotation.XmlElement;
036    import org.opengis.filter.expression.Expression;
037    
038    
039    /**
040     * Filter operator that checks if an expression's value is {@code null}.  A {@code null}
041     * is equivalent to no value present. The value 0 is a valid value and is not considered
042     * {@code null}.
043     *
044     * @version <A HREF="http://www.opengis.org/docs/02-059.pdf">Implementation specification 1.0</A>
045     * @author Chris Dillard (SYS Technologies)
046     * @since GeoAPI 2.0
047     */
048    @XmlElement("PropertyIsNull")
049    public interface PropertyIsNull extends Filter {
050            /** Operator name used to check FilterCapabilities */
051            public static String NAME = "NullCheck";
052        /**
053         * Returns the expression whose value will be checked for {@code null}.
054         */
055        @XmlElement("PropertyName")
056        Expression getExpression();
057    
058    }