Can someone explain to me which of the following two segments are correct?

        <nml:BidirectionalPort id="urn:ogf:network:netherlight.net:2013:port:a-gole:testbed:232">
            <nml:PortGroup id="urn:ogf:network:netherlight.net:2013:port:a-gole:testbed:232:in"/>
            <nml:PortGroup id="urn:ogf:network:netherlight.net:2013:port:a-gole:testbed:232:out"/>
        </nml:BidirectionalPort>

or

        <nml:BidirectionalPort id="urn:ogf:network:ampath.net:2013:ndn">
            <nml:name>ndn</nml:name>
            <nml:Port id="urn:ogf:network:ampath.net:2013:ndn-in"/>
            <nml:Port id="urn:ogf:network:ampath.net:2013:ndn-out"/>
        </nml:BidirectionalPort>

Should Port or PortGroup be used?  We have a mix right now in our topologies.

Thanks,
John