VEP-006: Discussion summary

[Markus Demleitner]

Dear Semantics community,

At the interop, we had a side meeting on VEP-006 (#calibration
definition).  I *think* we reached a sufficient consensus here, as
usual with some reservations.  I have tried to summarise the
discussion in VEP-006,
https://volute.g-vo.org/svn/trunk/projects/semantics/veps/VEP-006.txt

I'm also reproducing it below.  Do people feel their contributions
sufficiently considered and represented?  If not, what changes would
you like to see (direct commits to Volute cordially invited)?

Thanks,

             Markus

And here's VEP-006 as of rev. 5976:

Vocabulary: http://www.ivoa.net/rdf/datalink/core
Author: Markus Demleitner <msdemlei at ari.uni-heidelberg.de>
Date: 2020-09-09

Term: #calibration
Action: Modificiation
Label: Applicable Calibration
Description: Data products that can be used to remove instrumental
  signatures from #this.  Note that the calibration steps such data
  products feed have not been applied to #this yet.   To link
  calibration data already reflected in #this, use #progenitor.
Used-in: http://dc.g-vo.org/kapteyn/q/dl/dlmeta?ID=ivo%3A//org.gavo.dc/~%3Fkapteyn/data/fits/POT015_000317.fits

Term: #bias
Action: Modification
Description: Data products that can be used to remove detector offset levels 
  from #this.

Term: #dark
Action: Modification
Description: Data products that can be used to remove detector dark 
  current from #this.

Term: #flat
Action: Modification
Description: Data products that can be used to remove the signature of
  non-homogeneous detector sensitivity from #this.

Rationale: 
  In a discussion on the semantics mailing list (see
  http://mail.ivoa.net/pipermail/semantics/2020-June/002735.html
  and follow-ups) it was found that the existing descriptions of
  #calibration and its narrower terms are ambiguous; "resource used
  to calibrate" could mean both "resource that has been used" or
  "resource that can be used".  This VEP tries to make it clear that the
  "has been used" interpretation is for #progenitor, wheras #calibration
  is for "can be used".

Discussion:
  On the Semantics mailing list 
  (http://mail.ivoa.net/pipermail/semantics/2021-March/002774.html and
  followups), concerns were brought forward that excluding calibration
  data already applied would unnecessarily complicate the vocabulary;
  the temporal aspect ("has been applied" vs. "can be applied") should,
  if possible, be kept out of it.  Against that it was put forward that
  doing this would leave parts of #calibration within #progenitor (the
  "has been applied" part), other parts essentially in what some people
  suggested is #auxiliary (the "can be applied" part").  This violates
  the conditions for keeping the concepts organised in a tree, which
  was considered undesirable.

  On the other hand, it was recognised that being able to trace "science
  data" (as opposed to auxiliary resources like calibration data)
  through the provenance chain is valuable.  A method proposed to effect
  this, given that with VEP-006 #calibration is not available for this,
  could be to narrow the definition of #progenitor to "less calibrated
  science data".  But even if this step is not taken and #progenitor
  remains "anything upstream in the provenance chain", a new term
  #calibration-applied would seem useful (an example given was: when
  fusing 50 images, people want to tell those apart from, for instance,
  a master PSF that also went into the fusion).  Parties having use for
  such a concept are encouraged to author a VEP for it.

  In the end, after a side meeting at the May 2021 Interop consensus was
  found that #calibration should certainly not contain elements both in
  and outside of #progenitor; it was agreed that while, if we started
  again today, we would call the VEP-006 #calibration something like
  #calibration-applicable.  However, given the label is there, and that
  the level of detail below #calibration (with #bias, #dark, and #flat)
  probably mainly is useful (as far as datalink with its focus on
  actionable semantics is concerned) when a client wants to
  semi-automatically perform the calibration itself, it was decided that
  #calibration is kept with its label changed to "Applicable
  Calibration" and a corresponding definition.

  As we sharpen the definition of #auxiliary ("resources aiding the
  scientific exploitation of #this"), #calibration should probably
  become a child of it.  This, however, would be part of a VEP on
  #auxiliary.