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XML Pull parser library developed by Extreme Computing Lab, Indian University
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/*
 * $Header: /l/extreme/cvs/codes/xpp5/xis5/infoset_xpath_jaxen/org/xmlpull/infoset/xpath/jaxen/VariableContext.java,v 1.1 2005/05/16 23:59:18 aslom Exp $
 * $Revision: 1.1 $
 * $Date: 2005/05/16 23:59:18 $
 *
 * ====================================================================
 *
 * Copyright (C) 2000-2002 bob mcwhirter & James Strachan.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions, and the disclaimer that follows 
 *    these conditions in the documentation and/or other materials 
 *    provided with the distribution.
 *
 * 3. The name "Jaxen" must not be used to endorse or promote products
 *    derived from this software without prior written permission.  For
 *    written permission, please contact [email protected].
 * 
 * 4. Products derived from this software may not be called "Jaxen", nor
 *    may "Jaxen" appear in their name, without prior written permission
 *    from the Jaxen Project Management ([email protected]).
 * 
 * In addition, we request (but do not require) that you include in the 
 * end-user documentation provided with the redistribution and/or in the 
 * software itself an acknowledgement equivalent to the following:
 *     "This product includes software developed by the
 *      Jaxen Project (http://www.jaxen.org/)."
 * Alternatively, the acknowledgment may be graphical using the logos 
 * available at http://www.jaxen.org/
 *
 * THIS SOFTWARE IS PROVIDED ``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 THE Jaxen AUTHORS OR THE PROJECT
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, 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.
 *
 * ====================================================================
 * This software consists of voluntary contributions made by many 
 * individuals on behalf of the Jaxen Project and was originally 
 * created by bob mcwhirter  and 
 * James Strachan .  For more information on the 
 * Jaxen Project, please see .
 * 
 * $Id: VariableContext.java,v 1.1 2005/05/16 23:59:18 aslom Exp $
 */


package org.xmlpull.infoset.xpath.jaxen;

/** Resolves variable bindings within an XPath expression.
 *
 *  
 *  Variables within an XPath expression are denoted using
 *  notation such as $varName or $nsPrefix:varName, and may
 *  refer to primitive types (Boolean, Number or String),
 *  node-sets or individual XML nodes.
 *  
 *
 *  
 *  When a variable is bound to a node-set, the
 *  actual Java object returned should be a java.util.List
 *  containing XML nodes from the object-model (dom4j, JDOM, DOM, EXML)
 *  being used with the XPath.
 *  
 *
 *  
 *  A variable may validly be assigned the null value,
 *  but an unbound variable (one that this context does not know about)
 *  should cause an {@link UnresolvableException} to be thrown.
 *  
 *
 *  @see SimpleVariableContext
 *  @see NamespaceContext
 *
 *  @author bob mcwhirter
 *  @author James Strachan
 */
public interface VariableContext
{
    /** An implementation should return the value of an xpath variable
     *  based on the namespace uri and local name of the variable-reference
     *  expression.
     *
     *  
     *  It must not use the prefix parameter to select a variable,
     *  because a prefix could be bound to any namespace; the prefix parameter
     *  could be used in debugging output or other generated information.
     *  The prefix may otherwise be ignored.
     *  
     *
     *  @param namespaceURI  the namespace uri to which the prefix parameter
     *                       is bound in the xpath expression. If the variable
     *                       reference expression had no prefix, the namespace
     *                       uri is null.
     *  @param prefix        the prefix that was used in the variable reference
     *                       expression.
     *  @param localName     the local name of the variable-reference
     *                       expression; if there is no prefix, then this is
     *                       the whole name of the variable.
     *
     *  @return  the variable's value (which can be null)
     *  @throws UnresolvableException  when the variable cannot be resolved.
     */
    public Object getVariableValue( String namespaceURI,
                                    String prefix,
                                    String localName )
        throws UnresolvableException;
}