[Ops] Obscore: obs_id not null requirement

[Markus Demleitner]

Dear DAL, dear Ops,

[Ops: I'm cc-ing you because I'm linking to a praise of validation,
while the thread leading up to this is perhaps not very relevant to
you; discussion on obs_id should probably happen on DAL exclusively]

On Fri, Mar 04, 2022 at 11:43:29AM +0000, Mark Taylor wrote:
> I'm not generally in favour of MUST rather than SHOULD constraints
> for non-NULL column values, on the grounds that data producers
> who don't have sensible values to put in there may end up giving
> useless or nonsense values just to comply with the standards,
> which doesn't provide value to anybody.
> 
> However, it may be that the best answer to Markus's problem is
> for me to drop that taplint query, which could be reasonable.
> The intention is that taplint doesn't place unreasonable demands
> on the services that it validates, and I'm happy to take advice
> in cases where that's not happening.

When I tried to compose an answer to this this morning, I quickly
realised it was turning into a philosophical piece.  Which I then
turned into a blog post this afternoon:
<https://blog.g-vo.org/requirements-and-validators.html>

The TL;DR would be: Thanks, but no thanks.

Let's figure out whether we really have to require obs_id to be
non-NULL.  If we find a reason for that, I'll bite the bullet and
make the taplint query fast.  If we don't, let's drop the requirement
(I volunteer for writing an erratum, which should be quick and easy
after we've done the thinking here).

Thanks,

             Markus