Mapping of TAP_SCHEMA.columns.principal to SCS VERB

[Walter Landry]

Hi Everyone,

In the current TAP PR, TAP_SCHEMA.columns.principal is an integer.  Is
the intention to make that map to the same meaning as SCS's VERB?  It
seems that the meaning is somewhat inverted.  So

SCS VERB    TAP principal
1           2
2           1
3           0

If that is the case, should the meaning (and perhaps the actual
mapping) be put into the TAP PR?  To be concrete, the wording could be

  The "principal" number indicates the importance of a column. Clients
  can use this hint to make some columns visible, for example by
  selecting them by default in generating an ADQL query.  A value of
  '2' is for columns that the provider considers a bare minimum that
  are useful in describing the returned objects.  A value of '1' is
  for columns that may be generally useful, but not always necessary.
  A value of '0' is for columns that are probably only of use to
  specialized audiences.  These values correspond to VERB levels 1, 2,
  and 3 in Simple Cone Search (Plante & Molinaro et al 2017).

Thanks,
Walter Landry