SCS2

[gilles landais]

Hi all,

Thank you Markus for this initiative! I agree with DALI and Registry 
topics (and with P3T interface too).
I submit some of my first feedbacks.


Complying SCS with DALI is natural, but I think, we should also adapt 
(or focus) with the Simple and position Search Contexts.

First because implementing capabilities such as UPLOAD and asynchronous 
queries may become complex. Complex for users and complex for implementers.

For instance the Upload is a nice feature with possible optimization in 
case of multiples queries.
In an other hand, UPLOAD impacts the server architecture. It's an option 
in DALI : do we have to encourage this option ?

I am skeptical about using the asynchronous query for SCS. Indeed, 
cannot we expect for this kind of requests to be executed fast? Is async 
mandatory in DALI?

I would like also to ask for a bit of provenance in the output as 
specified in the DataOrigin Note. This feature is not currently in DALI 
- may be it should ?

Finally, position search is sometimes frustrating because the epoch. I 
suggest to find a way to provide the epoch (when applicable) of the 
datasets in output but also in the capabilities metadata (for instance 
in /tables).

use case: get a position from outside (for instance 2MASS in J2000) and 
then reuse position for gaia (in 2015.5). The information allows the 
user to make the change of coordinate system.


Regards,

Gilles Landais (CDS)


Le 17/09/2025 à 12:36, Markus Demleitner via dal a écrit :
> Dear DAL folks,
>
> I have procrastinated my College Park homework for a bit too long
> already, but now I just have to carve out some time for it: Cone
> Search 2.
>
> The main purpose of this will be to test strategies for major version
> transitions, but it is also a nice opportunity to explore how to
> opimally re-use what we already have in DALI, and of course SCS2
> itself should be (slight) progress over SCS1, too.
>
> I have just pushed a first commit drafting out the protocol itself,
> remaining as close to SCS1 (in concept) as possible (but not actually
> re-using significant amounts of texts):
> <https://github.com/msdemlei/scs2>.
>
> I am planning to write, over the next few weeks, sections on:
>
> * Registry aspects (stressing the importance of tablesets, also
>    mentioning the possibility of having auxiliary SCS capabilities)
> * Appendix A: Non-normative recommendations for clients
> * Appendix B: A transition plan
>
> Until that's done, I plan to not move this into ivoa-std und directly
> commit to main.  You'd be welcome to do the same; let me know and
> I'll add you as a collaborator.
>
> Once the basic text is there, I will of course move to ivoa-std and
> follow its rules.
>
> Still, even at this stage, collaborators and reviewers are most
> welcome.
>
> Thanks,
>
>            Markus
>