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SIAP-2.0 and SODA-1.0 cumulative "-Next" page.

  • Previous material
Old DAL future page :

IVOA note :

IVOA interop meetings presentation :

Paris :

College Park :

Victoria :

SIAP-2.0 feedback, issues and proposals

On GitHub:

  • input PARAMETERS with limited list of values : better description #1
Several SIAP2.0 parameters have a limited list of possible values – Some have lists limited by protocol (and obscore)

POL (Stokes, LINEAR, etc..) DPTYPE (image, cube, visibility, timeseries ;..) CALIB : levels FORMAT : fts, jpeg , png, etc..

– Some have free string values


– PARAMETERs less useful if we have no prior idea of their possible values. It often happens that services do not provide these lists of parameters although section 2.1.1 However Section 2.1.20 of SIAP2.0 states : Service PARAMETER self description Any service may include a DataLink service descriptor in the vOTable output to describe itself. this descriptor would describe the supported query parameters (standard and custom) including list of values for those with a fixed list (eg. COLLECTION INSTRUMENT FACILITY DPTYPE CALIB and FORMAT) *

This will allow to discover "possibilities" of the service prior to usage and optimize the queries

The "MAY" is obviously too weak. Version 2.1 could state SHOULD or MUST

  • No input PARAMETER exists to select the RELEASE DATE #2
ObsCore has an optional parameter "obs_release_date", but some projects complain no SIA PARAMETER allows to select on this.

Solution : create an OPTIONAL parameter to select on that ? What is the policy for OPTIONAL parameters ?

  • No Wild-carding of the input PARAMETERS values exists
SIAP2 PyVO interface developers and CADC complain that no wild-carding or incomplete strong value can be admitted in string parameter. Only exact matching.

What is the price to pay to add this functionality and how do we allow it ?

  • input PARAMETERS values are case sensitive #4
What is the price to pay to allow case-insensitive and how do we do that ?

  • POS=RANGE examples inconsistent with spec #5 (From Pat Dowler)
The spec clearly states that RA is in [0,360] and DEC is in [-90,90] but some POS=RANGE ... examples use -Inf and +Inf (probably copied the idea from use of open ended intervals in other params).

I consider this a bug in the example that should result in a fix and erratum because I recall we explicitly decided to not have services doing range reduction.

  • 1 shot discovery (and then access) to cutouts was possible in SIA1 but no more in SIA2 #6
SIAP1 had cut out and mosaic modes besides archive mode → 1 shot before access but only spatial We now have : SIAP2.0 or ObsTAP which deal with all axes

SODA : for cutouts only (all axes) +DataLink (Service descriptor and/or {links} table) → 2 shots before access (instead of 1)

Although it is pretty useful to have the 2 shots sometimes (allow the user to choose the actual limits according to ObsCore content and general context) there have been some complains (SkyView people for example also others) that the one-shot functionality disappeared. It would be perfectly possible to provide it by replacing the full retrieval or datalink url in access_url by a SODA url. SODA URL parameters are common with SIA. Where SIA Parameters values constrain the discovery, SODA parameters force the cutout dimensions.

A capability "virtual data generation" would have to be added to the service. If it exists how do we choose to provide these cutouts by a new "VIRTUAL" boolean parameter? Or by providing two lines in the response with the same obs_id ? The obscore values will be different, encluding publisher_did, but the observation will be the same

  • Possible confusion between FORMAT and RESPONSEFORMAT parameter #7
Alberto Micol 2019/03/&4 :

SIA specifies:

"The FORMAT parameter specifies response format(s) (the access_format column from the ObsCore [7] data model). This column describes the format of the response from the access_url (see 3.1.3) so the values could be data file types (e.g. application/fits) or they could be the DataLink [8] MIME type."

The initial part of the sentence mentions "response format(s)", which that greatly overlaps,

and generates confusion (at least in my mind), with the following DALI specification:

"The RESPONSEFORMAT parameter is used so the client can specify the format of the response (e.g. the output of the job)."

The SIA FORMAT and the DALI RESPONSEFORMAT are two different things, and I think that should be better clarified

in the text of the next SIA version. Could that be done?

  • SIA2 cannot discover rebinned data like SIA1 was able to do #8
Extending VIrtual SIAP2 as described in issue re-gridding/rebinning along a specific WCS can be done by adding this functionality to the virtual data discovery functionality described in issue #6. The access URL would be a SODA URL with the additional parameters proposed in SODA issue #4

An alternative is allowing SIA1 parameters of the MOSAIC mode to SIA2 interface

SODA-1.0 feedback, issues and proposals

On GitHub:

  • Wrong VOTAble syntax in polarization example #1
ON January the 16th 2020 Alberto Micol discovered :

Page 19 of the SODA standard shows:

'Polarization states to be extracted.

My understanding of the VOTable standard is that the correct way should instead be

(see the sentence

"All three MIN, MAX and OPTION sub-elements store their value corresponding to the minimum, maximum, or ``special value'' in a value attribute."

In the paragraph at: ):

Polarization states to be extracted.

Alberto is perfectly right !!!

  • Wrong example for BAND interval MIN and MAX values #2

This appeared in a discussion between Alberto Micol and Markus on the dal Mailing list

MIN and MAX cannot be single values as in the example It should be an array. But an array of what ?

An array of minimal values and an array of maximal values (Markus)

An array of minimal length interval and an array of maximal length interval (Alberto)

  • pixel cutouts (instead of world coordinates) on all axes are missing #3

Considered for version 1.0 but delayed to stay simple (due to syntax problems) Asked by CASDA , others Ranges can be given by SODA service descriptor or computed from ObsCore

Which syntax ?

  • No possibility to control output WCS by regridding/rebinning exists in SODA. #4

This was possible in SIA1.0 for the spatial axis (only) could be done by ADDing standard parameters to SODA for Spatial resolution : SPATRES Rotation : ROTA Sky Projection : PROJ or Alternatively by providing a WCS = (full text of WCS part of FITS header)

Skyview + CDS (SIA on top of Hips2FITS) have this functionality

Should we stabdardize it ? And If yes should we extend it to SIA2 in virtual mode (SIA issue #8) ? Or should we let it as a mixture of SIAP2 and SIAP1 parameters ?

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Topic revision: r3 - 2020-05-08 - FrancoisBonnarel
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