实在懒得打字，就把我在mailgroup里的内容贴过来吧，从http://issues.apache.org/jira/browse/IBATISNET-249 可以看到。
哈哈，突然看到自己的名字，好玩。用了人家的东西，也算做点贡献吧，开源还是不错的。
      When I tried to use "extends" in parameterMap nodes, but it can't work.
      Then I debug into ibatis.
      In DomSqlMapBuilder.cs line 1794, I found this line:
        XmlNode superNode = _configScope.SqlMapConfigDocument.SelectSingleNode(ApplyMappingNamespacePrefix(XML_SEARCH_PARAMETER)+ attributeExtendMap +"']", _configScope.XmlNamespaceManager );

          I think SqlMapConfigDocument should be instead by SqlMapDocument.
          After I Changed it into SqlMapDocument, it worked well.
         Is it a bug of iBatis.net or I make a mistake in my config file?
         In my book.xml file, just like
       <parameterMaps>
          <parameterMap id="BookInsert-params"  extends ="BookCommon_params">…..
             <parameterMap id ="BookCommon_params" class="Book">...
           </parameterMaps>