ant 中的 presetdef

<target name="UpdatePubsNested" description="update publications for an application using nested service element approach">
       <!--
             envName: required
             appPath: optional. If not used, it internally defaults to root path
             appName: required
             serverName: required
             businessName: optional. If not used, it means no change
             selected: optional. Valid values are true/yes or false/no, case-insensitive
                       if not used, it means publish or unpublish state has no change
       -->
       <check_property property="envName" />
       <check_property property="appPath" />
       <check_property property="appName" />
       <check_property property="serverName" />

       <check_property property="businessName" />
       <check_property property="selected" />
       <check_property property="serviceName" />
       <check_property property="action" />
       <check_property property="tagName" />
       <check_property property="tagValue" />

      <update_pubs
        envName="${envName}" appPath="${appPath}" appName="${appName}" serverName="${serverName}"
        businessName="${businessName}" selected="${selected}">

        <!--
            serviceName: optional. If not used, it means all the services under the application.
                         Wildcards are supported. * matches any sequence of chars, ? matches a single char.
                         multiple <service> elements are allowed under <update_pubs> element
        -->
        <service serviceName="${serviceName}">
          <!--
               action: required.  Valid values are save/remove, case-insensitive
               name: required
               value: required if action is save
               multiple <tag> elements are allowed under <service> element
           -->
          <tag action="${action}" name="${tagName}" value="${tagValue}"/>
        </service>
      </update_pubs>
</target>


<presetdef name="update_pubs">
    <UpdatePublications
      endpoint="${adminURL}/uddi_amxintg.httpbasic/services/UDDIUIService"
      username="${username}"
      password="${password}"
      output="" property="" format="xml"
      serviceName="*" businessName="" selected="" tags="">
    </UpdatePublications>
  </presetdef>



这个presetdef是什么意思，请大家帮帮忙