Vocabulary terms in MANGO

[Laurent Michel]

Dear Semantics,

[This message is related to https://github.com/ivoa-std/MANGO/issues/61]

I'm working on the draft of the MANGO data model:

   - https://github.com/ivoa-std/MANGO/
   - https://wiki.ivoa.net/twiki/bin/view/IVOA/MANGO-1_0

In some places, this model uses literal enumerations to specify some property roles:

     - Calibration level
     - Colour definition (magnitude ratio vs hardness ratio)
     - Shape definition (MOC, STCS...)
     - Possibly error distributions (poisson, gaussian...) (see issue #59)


This works fine, but has a major drawback: if some enumeration needs to be updated, we would have to create a new model version 
via a new RFC process. :-(

This issue has already been discussed in the IVOA and there was a consensus that vocabularies should preferably be used in data 
models AFAIR.

My questions are:
================

1) Do you still think it is better to replaces literal enumerations with a vocabulary?
2) Should this vocabulary be specific to MANGO or should it have a wider scope?
3) Should it be included in some existent IVOA vocabulary?
3) What is the process to create a new vocabulary (a simple VEP?)?

Laurent