content: /*
   * $Header$
   * $Revision$
   * $Date$
   *
   * ====================================================================
   *
   * Copyright 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:
   * 
   *   * Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   * 
   *   * 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.
   * 
   *   * Neither the name of the Jaxen Project nor the names of its
   *     contributors may be used to endorse or promote products derived 
   *     from this software without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   * IS" AND ANY EXPRESS 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 COPYRIGHT OWNER
   * OR 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 <bob@werken.com> and 
   * James Strachan <jstrachan@apache.org>.  For more information on the 
   * Jaxen Project, please see <http://www.jaxen.org/>.
   * 
   * $Id$
   */
  
  
  package org.jaxen;
  
  /** Resolves variable bindings within an XPath expression.
   *
   *  <p>
   *  Variables within an XPath expression are denoted using
   *  notation such as <code>$varName</code> or 
   *  <code>$nsPrefix:varName</code>, and may
   *  refer to a <code>Boolean</code>, <code>Double</code>, <code>String</code>,
   *  node-set (<code>List</code>) or individual XML node.
   *  </p>
   *
   *  <p>
   *  When a variable is bound to a node-set, the
   *  actual Java object returned should be a <code>java.util.List</code>
   *  containing XML nodes from the object-model (e.g. dom4j, JDOM, DOM, etc.)
   *  being used with the XPath.
   *  </p>
   *
   *  <p>
   *  A variable may validly be assigned the <code>null</code> value,
   *  but an unbound variable (one that this context does not know about)
   *  should cause an {@link UnresolvableException} to be thrown.
   *  </p>
   *  
   *  <p>
   *  Implementations of this interface should implement <code>Serializable</code>.
   *  </p>
   *
   *  @see SimpleVariableContext
   *  @see NamespaceContext
   *
   *  @author <a href="mailto:bob@werken.com">bob mcwhirter</a>
   *  @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
   */
  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.
       *
       *  <p>
       *  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.
       *  </p>
       *
       *  @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 <code>null</code>.
       *  @param prefix        the prefix that was used in the variable reference
       *                       expression; this value is ignored and has no effect
       *  @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 <code>null</code>)
       *  @throws UnresolvableException  when the variable cannot be resolved
       */
      public Object getVariableValue( String namespaceURI,
                                      String prefix,
                                      String localName )
          throws UnresolvableException;
  }
  