Obscore: obs_id not null requirement

[Patrick Dowler]

On Mon, 14 Mar 2022 at 04:44, Markus Demleitner <
msdemlei at ari.uni-heidelberg.de> wrote:

>
> On Mon, Mar 07, 2022 at 12:41:04PM -0800, Patrick Dowler wrote:
> > Having said that, this has a clear meaning to me because our ObsCore impl
> > is a view on CAOM and CAOM is normalised wrt. this obs_id concept (where
> > ObsCore is denormalised), but I expect it is not so simple to specify use
> > of nulls here and clearly deal with other variations of underlying
> models.
>
> I have to admit I don't quite get what you're saying here -- is this
> a consideration that having obs_id non-NULL makes it easier to have
> it as a view over larger DMs?  If so, I'd need a bit more
> explanation: Is it that CAOM consumers had a more difficult time
> consuming obscore?  But why would they even try to consume obscore?
> Or am I speculating in the entirely wrong direction?


I guess what I am saying is that CAOM is normalised compared to ObsCore:
there is an
"observation" table where obs_id is the primary key, another table where
obs_id is a
foreign key, and the ObsCore view is a join of these two tables. So obs_id
is never null (fine)
and the "part of this group" meaning in ObsCore has a very specific meaning
from the CAOM
model (the relationship between those two tables aka relation between those
two
classes). There are other ways to define "part of this group" that are more
vague than the meaning
in CAOM and I wonder how tightly we need to define it.

In CAOM, it is 1 Observation -> N Plane, where each plane is a "product"
(most common case is
different calibration levels but sometimes different/alternate processing)
and it is a composition relation
in the model. For users, it is the direct "these have the same photons"
meaning and that's more specific than
"part of a group".

I am certain this was the intent for obs_id when ObsCore was created. The
name (obs_id) implies the same
1 observation -> N ObsCore records.Do we need to define obs_id that
specifically or just vaguely? Vaguely
doesn't really tell users what they can or should not do (eg they should
not stack two images with the same
obs_id together if it is the same photons).

hope that helps,

--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada




> Thanks,
>
>            Markus
>
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