compound identifiers for resources?

[caindy]

Related to #9 and #6, we had the following question in the webinar (paraphrased):

Branches in our system model are nominated by a "From Bus" and a
"To Bus"; they are not assigned a (synthetic) unique identifier. How will we
be used the "resource-id" field to identify a branch when branches are not
assigned a single identifier?

Initial thoughts:

• We could recommend an approach that uses an internal identifier a la RDF along with "from" and "to" alternate names.
• Consider simply using "{fromBus} {toBus}" as the primary identifier in this case.
• It's possible to have two (rarely three) circuits between the same two busses, in which case they are ostensibly assigned circuit ids.
• Having a way to designate the from bus and to bus could be generally useful in some debugging and support scenarios.