About adding prerequisites to plugin.xml when useing JFS

I am using Jazz Foundation Server SDK to dev a rest service
how can i add required services in the plugin.xml?

The plugin.xml is:

<plugin>

   <extension

         point="com.ibm.team.jfs.app.restServices">

      <restService

            alias="helloworld"

            class="com.example.helloworld.HelloWorld"

            displayName="Hello World Handler">

      </restService>

   </extension>

</plugin>

I want to add this:

<prerequisites>

   <requiredService interface="com.example.hellobaby.service">

 </prerequisites>

<prerequisites>'s parent elament should be?

thanks