Small question/suggestion re: ObsCore

[Gregory Dubois-Felsmann]

In the context of implementing application behavior associated with ObsCore-style data tables, I noticed the following thing:

The ObsCore 1.1 standard, in Appendix C, Table 6, specifies the UCDs to be associated with ObsCore columns.  In particular, for s_ra and s_dec, it suggests pos.eq.ra and pos.eq.dec.  

Section 4.22 of the standard says "Service providers may include additional columns in the ivoa.ObsCore table to expose additional metadata. These columns must be described in the TAP_SCHEMA.columns table […]”.

This means that it’s possible that additional columns with UCD “pos.eq.ra”, say, might be added.

From the perspective of a client application, it might still want a hint as to which “pos.eq.*” columns pair is “authoritative” or “principal” in some way.  This is what the “meta.main” secondary UCD is meant to capture.  Certainly a client application could decide to resolve the ambiguity by favoring the pair with column _names_ “s_ra”, “s_dec”.   However, if we are already building our clients to respect “meta.main” as a hint as to which columns to prioritize:

Was it considered, or would it be appropriate, for a service returning an ObsCore-compliant table (e.g., an SIAv2 or ObsTAP service) to be required (or strongly recommended) to include “meta.main” in the UCDs for “s_ra” and “s_dec”?

Thanks,

Gregory