[Nml-wg] Transitivity of hasPort
Freek Dijkstra
Freek.Dijkstra at sara.nl
Fri Aug 7 08:04:44 CDT 2009
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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