Mapping of TAP_SCHEMA.columns.principal to SCS VERB

[Markus Demleitner]

Hi,

On Mon, Oct 09, 2017 at 03:32:40PM -0700, Walter Landry wrote:
> 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

Hm -- frankly, I think I'd like that.  I'm always fond of
streamlining things between the various protocols.

The question is: Will this break any client?  And if it were, would
the breakage be serious?

Client writers: Do you do anything with principal?

The very least we could do in 1.1 is prepare for this move and say
something like "clients should compare against zero and non-zero,
never against 1, as future versions of this standard may assign
additional semantics to different non-zero values".

          -- Markus