pdowler
commented
3 years ago The current spec allows the service implementation to reject multiple params so that provider can put a limit on how complex output should be. At CADC we limit SODA-sync to single value for each param and we limit SODA-async to a single ID value but allow multiple "cutout" values and perform the cartesian product.
It will always be complex and require arbitrary packaging for sync to support multiple params. The CADC implementation could allow it and produce MEF files but it introduces a subtle complexity that I didn't really like: if you do 2 POS cutouts from a simple FITS file, you could implement that do do anyo one of these:
- create an MEF with one extension per POS, but the you have to fabricate a sensible primary header (cannot just keep all the cards in the original one)... conceptually I didn't like simple to mef
- create another simple mef with a sparse data array and both POS(s)... but that is much larger than necessary if the two POS values are ~far apart and doesn't give the caller what they asked for: two cutouts
- create a package (eg tar) with multiple simple fits files in it)... have written code to create tar on the fly and CADC could do this, but then you get in the situation where some requests to SODA-sync return FITS and others return TAR. Plus on-the-fly package has all kinds of operational complexity (files stored in different locations because of a distributed storage arch is the one we have and don't like at all)
I'm sure there are more ways to do it with their pros and cons. Mostly you probably end up with different behaviour from different providers and that's bad for users. So, my feeling now is that SODA-sync should have explicitly only described/specified a single cutout (one value of each cutout param). Since SODA-async has the facility to manage multiple results I don't think inventing a way to do it in SODA-sync adds much.
molinaro-m
Bonnarel
robertbutora
When several of the PARAM queries (POS, BAND, etc...) are multiple we are facing a cartesian product issue : how do we retrieve all these results. Seems to be easy in async mode which is built to manage multiple results ? But in sync ? MEF formats ? archive files ? VOTable contaning pointers ? What about using UPLOAD functionality (DALI, 3.4.5 UPLOAD) for this ?