RDF regards an NML relations as any other property. In order to distinguish in RDF between 

    <nml:Relation type="http://schemas.ogf.org/nml/2013/10/base#hasInboundPort">
and
    <nml:hasInboundPort>

Propose: RDF needs to add the following triplet for all NML relations:
    nml:hasInboundPort rdfs:subPropertyOf nml:Relation .

Note: a NML version 1 compliant client does not need to add the these triplets for relations defined in version 1 of NML
, but it MUST include them for other relations if they are used in the description. Eg. if it is using a relation 
defined in the experimental extension schema.


Example 1: the following two syntaxes are equivalent.

RDF:

 @prefix nml: <http://schemas.ogf.org/nml/2013/10/base#>; .
 nml:hasInboundPort rdfs:subPropertyOf‎nml:Relation .
 urn:ogf:network:example.net:2012:mynode a nml:Node .
 urn:ogf:network:example.net:2012:mynode nml:hasInboundPort urn:ogf:network:example.net:2012:myport .
 urn:ogf:network:example.net:2012:myport a nml:Port .

XML:

 <nml:Node id="urn:ogf:network:example.net:2012:mynode">
   <nml:Relation type="http://schemas.ogf.org/nml/2013/10/base#hasInboundPort">
     <nml:Port idRef="urn:ogf:network:example.net:2012:myport" />
   </nml:Relation>
 </nml:Node>

Example 2: the following two syntaxes are equivalent (note the missing "nml:hasInboundPort rdfs:subPropertyOf‎nml:
Relation ." line)

RDF:

 @prefix nml: <http://schemas.ogf.org/nml/2013/10/base#>; .
 urn:ogf:network:example.net:2012:mynode a nml:Node .
 urn:ogf:network:example.net:2012:mynode nml:hasInboundPort urn:ogf:network:example.net:2012:myport .
 urn:ogf:network:example.net:2012:myport a nml:Port .

XML:

 <nml:Node id="urn:ogf:network:example.net:2012:mynode">
   <nml:hasInboundPort">
     <nml:Port idRef="urn:ogf:network:example.net:2012:myport" />
   </nml:hasInboundPort>
 </nml:Node>