[Nml-wg] Adaptation between Links

[Freek Dijkstra]

Jason Zurawski wrote:

> I could see the shortcut notation being made available through an
> extension (e.g. nml-lazy), but too many options will confuse things. 

I would prefer this in the main document, but have no objections in
putting this in another document and/or specifying that it does not need
to be supported by a "base" NML implementation.

We can't put it this in a different (e.g. nml-lazy) namespace though.
The simple reason is that this is a relation, and relation types have no
namespace.

How to deal with extensions, such as this one, is exactly the question
that I brought up earlier today
(http://www.ogf.org/pipermail/nml-wg/2012-May/000955.html).

In particular -- do we want to limit the number of relation types for
NML 1? Or can we extend that without changing the NML schema itself?

Also, do we want to add a namespace to relation types after all so we
can differentiate between "base" NML extension and e.g. "nml-lazy"
extensions?

> If
> there was the ability to capture the 16 object interaction in 3 objects,
> why would you ever waste time encoding it as such?

Because there is different needs what is to be described. The 8 objects
+ 8 relations allow naming of Ports, and specification of the type of
adaptation used. The 2 objects + 1 relation does not allow that.

Note that we have a similar situation for isSerialCompoundLink. It is
perfectly possible to reason that a serial compound link exists by
following all isSource and isSink relations. The isSerialCompoundLink is
just shorter, because it does not list ports. (Admittedly,
isSerialCompoundLink also allows one to name an end-to-end link. This
providesLink proposal does not have such advantage. It's only shorter,
no other advantages.)

Freek

> 
> Thanks;
> 
> -jason
> 
> On 5/10/12 7:41 AM, thus spake Freek Dijkstra:
>> I've just created a new artifact,
>> https://forge.ogf.org/sf/go/artf6507
>>
>> Here is the full proposal.
>>
>>
>> Adaptation is between Ports, and requires the following objects:
>> * 2 Link instances
>> * 4 Port instances
>> * 2 Adaptation instances
>> * 8 relations between these instances
>> (see https://forge.ogf.org/sf/go/artf6514 for details)
>>
>> While the above is great to describe a topology in detail, it is
>> sometimes useful to describe less detail.
>>
>> I propose a shortcut to define adaptation between Links:
>>    Link --(providesLink)-->  Link
>>
>> This would only require the following objects:
>> * 2 Link instances
>> * 1 relation between these instances
>>
>> This is similar how isSerialCompoundLink also relates Link objects,
>> bypassing the more tedious Link<--(isSink)-- Port --(isSource)-->  Link
>> relations.
>>
>> Of course this is less detailed (e.g. it is not possible to describe the
>> type or adaptation, or the name of the Ports). It's intended use is a
>> situations where a full topology description (with all ports) is not
>> required or not desirable.
>>
>> NML:
>>
>>    Link --(providesLink)-->  Link
>>
>> The subject (Link on the left) is on the server layer. The link of the
>> right (the object) is one the client layer, and
>> source and sinks of both Links MUST be related with an equal adaptation
>> stack. In other words, both Links MUST span the
>> same distance.
>>
>> For example, in the following ASCII-art, the following statements are
>> True:
>>    l0 --(providesLink)-->  l1     - True
>>    l0 --(providesLink)-->  l2-2   - True
>>    l1 --(providesLink)-->  l2-2   - True
>> While the following statements are all False:
>>    l0 --(providesLink)-->  l3     - False
>>    l1 --(providesLink)-->  l3     - False
>>    l2-2 --(providesLink)-->  l3   - False
>>
>>                              l3
>>    O ----------------------------------------------->  O
>>    |                                                  |
>>    _                                                  _
>>    V                                                  V
>>    |      l2-1              l2-2             l2-3     |
>>    O ------------->  O ------------->  O ------------->  O
>>                     |                |
>>                     _                _
>>                     V                V
>>                     |       l1       |
>>                     O ------------->  O
>>                     |                |
>>                     _                _
>>                     V                V
>>                     |       l0       |
>>                     O ------------->  O
>>
>>  From these requirements follows that the subject is always a terminated
>> network connection (thus not a segment of a
>> larger link connections), while the object is never a serial compound
>> link.
>>
>> XML example:
>>
>>    <nml:Link
>> id="urn:ogf:network:example.net:2012:link:fiber:NOR:xe-1-1-0:AMS:xe-2-1-0:1530nm">
>>
>>      <nml:name>1530nm wave between NOR and AMS</nml:name>
>>      <nml:Relation type="providesLink">
>>        <nml:Port
>> idRef="urn:ogf:network:example.net:2012:link:eth:NOR-AMS-0001" />
>>      </nml:Relation>
>>    </nml:Service>
>>
>> RDF example:
>>
>>    @prefix nml:<http://example.ogf.org/schemas/nml/>; .
>>    @prefix nmlrel:<http://example.ogf.org/schemas/nml-relation/>; .
>>    @prefix ex:<urn:ogf:network:example.net:2012>  .
>>
>>    ex:link:fiber:NOR:xe-1-1-0:AMS:xe-2-1-0:1530nm a nml:Link ;
>>      nml:name "1530nm wave between NOR and AMS" ;
>>      nmlrel:providesLink ex:link:eth:NOR-AMS-0001 .