[Nml-wg] Transitivity of hasPort

[Guy Roberts]

I vote for option 3, it makes the most sense to me.

Guy

-----Original Message-----
From: Freek Dijkstra [mailto:Freek.Dijkstra at sara.nl] 
Sent: 07 August 2009 14:05
To: Network Markup Language Working Group
Subject: [Nml-wg] Transitivity of hasPort

Freek Dijkstra wrote (in "Use case: cross connect (single layer)"):

> Here is the use case of the cross connect (single layer).

Paola Grosso wrote:

> - Transitivity of relation, such as if a device is at one Location, all
> its Ports are at the same location. Should transitivity specified in the
> model or implicit?

The problem I had is there there were 16 "hasPort" relations for 8 
unidirectional ports: a hasPort relation between the Node and each port, 
and a hasPort relation between the SwitchMatrix Service and each port.
In the call I wondered if this can be an implicit relation.

I recently thought about this, and it seems we have 3 options:
1) No transitivity:
You have to specify all 16 "hasPort" relation, as in the example I sent 
out previous week.

2) Transitivity from Node to Service:
If there is a hasPort relation between a Node and a Port, and also a 
hasService between the same Node and a Service, then it is implied that 
there is also a hasPort relation between the Service and the Port, 
_provided that the Port is on the same layer as the Service_. This 
scenario was discussed in the call, and we added this condition to cope 
with Nodes with services on multiple layers.

3) Transitivity from Service to Node:
If there is a hasPort relation between a Service and a Port, and also a 
hasService between a Node and the same Service, then it is implied that 
there is also a hasPort relation between the Node and the Port.

This last scenario was not discussed, but I think it makes more sense: 
this way we would not need the additional condition that the Port is on 
the same layer as the Service.
Less conditions = better.

Regards,
Freek
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