本文档讲解了OTA的概念

				package org.kxml;
				
				import java.util.*;
				
				/** Like Attribute, this class is immutable for similar reasons */
				
				public class PrefixMap {
				
				    public static final PrefixMap DEFAULT = new PrefixMap (null, "", "");
				
				    String prefix;
				    String namespace;
				    PrefixMap previous;
				
				
				    public PrefixMap (PrefixMap previous, String prefix, String namespace) {       
					this.previous = previous;
					this.prefix = prefix;
					this.namespace = namespace;
				    } 
				
				
				    public String getNamespace () {
					return namespace;
				    }
				
				    public String getPrefix () {
					return prefix;
				    }
				
				    public PrefixMap getPrevious () {
					return previous;
				    }
				
				    /** returns the namespace associated with the given prefix,
					or null, if none is assigned */
				
				    public String getNamespace (String prefix) {
					PrefixMap current = this;
					do {
					    if (prefix.equals (current.prefix)) return current.namespace;
					    current = current.previous;
					}
					while (current != null);
					return null;
				    }
				
				
				    public String getPrefix (String namespace) {
					PrefixMap current = this;
					
					do { 
					    //System.err.println ("found: "+current.namespace +"/"+ current.prefix + "/" +getNamespace (current.prefix));
					    if (namespace.equals (current.namespace)
						&& namespace.equals (getNamespace (current.prefix))) 
						return current.prefix;
				
					    current = current.previous;
					}
					while (current != null); 
					return null;
				    }
				}