[Nml-wg] Session notes for NML

[Freek Dijkstra]

Members of the NML working group joined for two sessions at OGF 32.
About 15 participants attended the sessions.

Here are some notes; note that they are not complete (Jerry created some
additional notes during the 1st session). However, I'll post them here
now before I forget... :)

At the first session, Jeroen van der Ham went through the RNC schema,
explaining and correcting minor issues.

The main topic on the table was the XML syntax for describing ordered lists.
After some heated discussions, the participants agreed on the following
syntax for an example of a link "link_A-to-C" is described as the
concatenation of two smaller segments, "link_A-to-B", followed by
"link_B-to-C".

  <nml:link id="urn:ogf:network:example.net:link_A-to-C">
    <nmlserialcompound:relation type="serialcompound">

      <nml:link idRef="urn:ogf:network:example.net:link_A-to-B">
        <nml:relation type="next">
          <nml:link idRef="urn:ogf:network:example.net:link_B-to-C" />
        </nml:relation>
      </nml:link>

      <nml:link idRef="urn:ogf:network:example.net:link_B-to-C">
      </nml:link>

    </nmlserialcompound:relation>
  </nml:link>

A few notes are in place here:
* As agreed earlier, the syntax does not rely on the order of the XML
elements in the syntax (while most parser retain the order, this is not
required by the XML specification.) Indead, the "next" relation is used
to explicitly specify the order.
* No explicit "first" or "last" element is specified. A "last" element
in a list can be found by finding the item without a "next" relation. A
"first" item in a list can be found by finding the only item in the list
which has no pointer to it.
* There can be only one "first" and "last" element in a list; this means
that branching (e.g. an item with two "next" items) is not allowed; this
should be described with another construct.
* This means that
* while it was argued that the "next" relation is a syntax construct,
while the relations as defined in the NML UML schema are topology
constructs, and thus different, the same syntax would be used to
describe both relations.
* The name of the topological relation in the above example is called
"serialcompound" after Figure 10 of G.805 (of Figure 16 of G.800). The
name was not great, but the participants were too tired to come up with
something better :)
* The ordered list on itself is not enclosed in it's own XML tag (like
<nml:list>), the elements are direct subelements of the parent
<relation> tag.

* At the end of the session, the participants had a discussion how to
encode the relation type. In the above example, it is listed as
'<nmlserialcompound:relation type="serialcompound">' and '<nml:relation
type="next">'. While some arguments where laid forward, no definitive
conclusion was reached. This topic remains open for discussion>.

Finally, I like to thank all contributors to the discussion. It may have
taken some time to talk some sense in me, that was due to my
stubbornness, not due to the quality of the arguments. Those were in my
opinion particularly good. A particular thanks to Jeff, Jason and Jeroen
(the 3 J's) is certainly in place.

Thanks,
Freek