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Dear Apps and VOTable users,<br>
<br>
After reading the proposed new version of VOTable, I have a few
questions about the essential changes in this version changes in
this versions. Version 1.5 of VOTable introduces an alternative
way of associating columns with a coordinate system.<br>
<br>
For VOTable versions 1.0, 1.1, 1.3 and 1.4, the COOSYS for a given
field is defined using the ref attribute of FIELD, which points to
the ID of the COOSYS concerned (<b><font color="#8000ff">FIELD ref
-> COOSYS ID</font></b>). The role of each field
(ra,dec,pmra, pmdec, rv...) is determined by the attributes of
each FIELD (ucd, unit, utype). Cf example A - below. And this
method has been extended to the definition of the TIMESYS in
version 1.4 of VOTable.<br>
<br>
The WD 1.5 introduces an alternative mode of "reverse"
association, from the COOSYS definition to the fields by using
FIELDref (and PARAMRef), associated with the COOSYS, and pointing
to the FIELD IDs concerned (<b><font color="#ff8040">COOSYS/FIELDREF
ref -> FIELD ID</font></b>). The role is determined by an
associated utype to the FIELDref (or PARAMref) - the rest of the
metadata whose unit remains described in the FIELD (possibly
necessary to determine the exact interpretation of the column -
ex:distance vs parallax)<br>
<br>
If I have understood correctly the proposal, this method uses the
same principles as those already proposed and validated in VOTable
1.2 (2009), which referred to the IVOA note "2009 - Referencing
STC in VOTable v1.1" =>
<a class="moz-txt-link-freetext" href="https://www.ivoa.net/documents/Notes/VOTableSTC/NOTE-VOTableSTC-1.1-20090612.html">https://www.ivoa.net/documents/Notes/VOTableSTC/NOTE-VOTableSTC-1.1-20090612.html</a>,
then v2.0 (2010) (see example C) with the difference that the
COOSYS had been replaced by a GROUP and different utypes have been
proposed. As a reminder, this method was subsequently deprecated
because no VOTable provider had implemented it - even several
years after its adoption. Version 1.3 (2013) of VOTable then
reverted to the original COOSYS method in order to avoid VOTables
no longer having any coordinate system definition.<br>
<br>
This proposal in 1.5 is more flexible than version 1.2 (which
completely eliminated the use of COOSYS). The fact remains that
having 2 association methods still poses consistency questions?
Which is required, which is optional? What should be done when the
2 methods are simultaneously present, but not consistent? Should
we expect the original referencing to disappear (FIELD ref ->
COOSYS ID)? What are the consequences? what are the benefits? Will
this new referencing method be extended to TIMESYS? ... <br>
<br>
The discussion on this evolution of VOTable 1.4 -> 1.5 - which
may seem minor, but can have major consequences - can only be
found on github (started at the end of June 2023 =>
<a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/pull/40">https://github.com/ivoa-std/VOTable/pull/40</a>), and relatively few
people have reacted since then. Would it be possible to use the
Apps IVOA mailing list to reach a wider audience.<br>
<br>
Best regards<br>
Pierre Fernique<br>
<br>
<br>
<b>A) Original method: </b><b><br>
</b><br>
<font face="monospace"><VOTABLE version="1.4" ...><br>
<RESOURCE><br>
<COOSYS <font color="#8000ff"><b>ID="icrs"</b></font>
system="ICRS"/><br>
<PARAM name="pmra" utype="votable:ProperMotion-lon" <b><font
color="#8000ff">ref="icrs"</font></b> ucd="pos.pm;pos.eq.ra"
unit="mas/yr"<br>
datatype="float" value="123.45"/><br>
<PARAM name="pmdec" utype="votable:ProperMotion-lat" <b><font
color="#8000ff">ref="icrs"</font></b>
ucd="pos.pm;pos.eq.dec" unit="mas/yr"<br>
datatype="float" value="321.09"/><br>
<TABLE name="pos"><br>
<FIELD name="ra" <b><font color="#8000ff">ref="icrs"</font></b>
datatype="double" ucd="pos.eq.ra" unit="deg"/><br>
<FIELD name="dec" <font color="#8000ff">ref="icrs"</font>
datatype="double" ucd="pos.eq.dec" unit="deg"/><br>
<DATA><br>
<TABLEDATA><br>
<TR><br>
<TD>121.2846388435</TD><br>
<TD>-33.9221492345</TD><br>
</TR><br>
</TABLEDATA><br>
</DATA><br>
</TABLE><br>
</RESOURCE><br>
</VOTABLE></font><br>
<br>
<b>B) Proposed alternative for WD 1.5:</b><b><br>
</b> <i>(example from the WD 1.5, with additions of the
original reference method (in italic) )</i><br>
<b><br>
</b><br>
<font face="monospace"><VOTABLE version="1.5" ...><br>
<RESOURCE><br>
<COOSYS <b><font color="#8000ff">ID="system"</font></b>
system="ICRS"><br>
<FIELDref utype="votable:LonLatPoint-lon" <b><font
color="#ff8040">ref="id-1"</font></b>/><br>
<FIELDref utype="votable:LonLatPoint-lat" <b><font
color="#ff8040">ref="id-2"</font></b>/><br>
<PARAMref utype="votable:ProperMotion-lon" <b><font
color="#ff8040">ref="id-3"</font></b>/><br>
<PARAMref utype="votable:ProperMotion-lat" <b><font
color="#ff8040">ref="id-4"</font></b>/><br>
</COOSYS><br>
<PARAM name="pmra" <b><font color="#ff8040">ID="id-3"</font></b>
<i><b><font color="#8000ff">ref="system" </font></b></i>ucd="pos.pm;pos.eq.ra"
unit="mas/yr"<br>
datatype="float" value="123.45"/><br>
<PARAM name="pmdec" <b><font color="#ff8040">ID="id-4"</font></b>
</font><font face="monospace"><font face="monospace"><i><b><font
color="#8000ff">ref="system" </font></b></i></font>ucd="pos.pm;pos.eq.dec"
unit="mas/yr"<br>
datatype="float" value="321.09"/><br>
<TABLE name="pos"><br>
<FIELD name="ra" <b><font color="#ff8040">ID="id-1"</font></b>
</font><font face="monospace"><font face="monospace"><i><b><font
color="#8000ff">ref="system" </font></b></i></font>datatype="double"
ucd="pos.eq.ra" unit="deg"/><br>
<FIELD name="dec" <b><font color="#ff8040">ID="id-2"</font></b>
</font><font face="monospace"><font face="monospace"><i><b><font
color="#8000ff">ref="system" </font></b></i></font>datatype="double"
ucd="pos.eq.dec" unit="deg"/><br>
<DATA><br>
<TABLEDATA><br>
<TR><br>
<TD>121.2846388435</TD><br>
<TD>-33.9221492345</TD><br>
</TR><br>
</TABLEDATA><br>
</DATA><br>
</TABLE><br>
</RESOURCE><br>
</VOTABLE><br>
<br>
</font><br>
<b>C) Method used in REC 1.2 (referencing the "STC note in VOTable
1.1"), and deprecated in REC 1.3</b><b><br>
</b><i>(example from the STC note as is)</i><b><br>
</b><br>
<font face="monospace"><TABLE><br>
<GROUP <b><font color="#8000ff">ID="Coo1"</font></b>
utype="stc:AstroCoords" ><br>
<PARAM name="cooframe" datatype="char" arraysize="*"
ucd="pos.frame"<br>
utype="stc:AstroCoords.coord system id"<br>
value="UTC-ICRS-TOPO" /> <!-- UTC-ICRS-TOPO defined
in STC-Lib --><br>
<FIELDref <b><font color="#ff8040">ref="ObsStart"</font></b>
/> <!-- second referencing, optional --><br>
<FIELDref <b><font color="#ff8040">ref="RAJ2000"</font></b>/>
<!-- second referencing, optional --><br>
<FIELDref <b><font color="#ff8040">ref="DEJ2000"</font></b>/>
<!-- second referencing, optional --><br>
</GROUP><br>
<FIELD name="RAJ2000" ucd="pos.eq.ra;meta.main" <b><font
color="#8000ff">ref="Coo1"</font></b><br>
<b><font color="#ff8040">ID="RAJ2000"</font></b>
utype="stc:AstroCoords.Position2D.Value2.C1"<br>
datatype="float" precision="4" unit="deg" /><br>
<FIELD name="DEJ2000" ucd="pos.eq.dec;meta.main" <b><font
color="#8000ff">ref="Coo1"</font></b><br>
<b><font color="#ff8040">ID="DEJ2000"</font></b>
utype="stc:AstroCoords.Position2D.Value2.C2"<br>
datatype="float" precision="4" unit="deg" /><br>
<FIELD name="ObsStart" ucd="time.start;obs" datatype="char"
xtype="iso8601"<br>
arraysize="19" unit="s" <b><font color="#ff8040">ID="ObsStart"</font></b>
<b><font color="#8000ff">ref="Coo1"</font></b><br>
utype="stc:AstroCoords.Time.TimeInstant.ISOTime" /><br>
<FIELD name="ExpTime" ucd="time.duration;obs.exposure"<br>
datatype="float" width="6" precision="1" unit="s"/><br>
<DATA><br>
...<br>
</TABLE><br>
</font><br>
</p>
<div class="moz-cite-prefix">Le 14/09/2023 à 14:41, Tom Donaldson a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:A467E18D-8C4E-4023-8DA1-D3801C3F837D@stsci.edu">
<pre class="moz-quote-pre" wrap="">Dear VOTable Enthusiasts,
On behalf of the Applications Working Group I’m pleased to announce the first Working Draft for VOTable version 1.5. The document can be found here: <a class="moz-txt-link-freetext" href="https://www.ivoa.net/documents/VOTable/20230913/">https://www.ivoa.net/documents/VOTable/20230913/</a>
Summary of changes since version 1.4
--------------------------------------------------
- Schema changes:
--- COOSYS now has a refposition attribute analogous to TIMESYS
--- COOSYS system now uses vocabularies
--- ** COOSYS now allows FIELDref and PARAMref children for the specific purpose of building propagatable positions
- Clarifications/rewording on:
--- meaning of MIN/MAX value attributes for array types.
--- removing the "recommendation" to use xmlns to do utype prefix binding.
--- timescales for calendar epochs
--- ID/ref positioning advice
** - The COOSYS changes to handle propagation of positions are the most substantial proposed changes in this release. For additional information, see:
- Discussion in the PR: <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/pull/40">https://github.com/ivoa-std/VOTable/pull/40</a>
- Draft PR in Astropy showing how this could be used: <a class="moz-txt-link-freetext" href="https://github.com/astropy/astropy/pull/14992">https://github.com/astropy/astropy/pull/14992</a>
The changes since version 1.4 were all made via Github pull requests. Some of these PRs contain useful discussion of the details so can be a useful reference for the ongoing Working Draft discussion. The complete list of PRs included in this working draft can be found here: <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/pulls?q=is%3Apr+is%3Aclosed+milestone%3Av1.5">https://github.com/ivoa-std/VOTable/pulls?q=is%3Apr+is%3Aclosed+milestone%3Av1.5</a>
Review and Comment
-----------------------------
Our job now is to review the document and propose/implement any changes needed. The primary forum for discussion will be the Applications WG mailing list (<a class="moz-txt-link-abbreviated" href="mailto:apps@ivoa.net">apps@ivoa.net</a>). Github Pull Requests and Issues also offer a nice interface for discussion, so I recommend using those for discussing concrete or specific change proposals. For example, instead of commenting on the mailing list that a particular paragraph should be different, submitting a Pull Request with the specific change in context can be a productive way to further the conversation. If you have concrete proposals and would like help with creating a PR, just let us know on the Apps list and one of the editors will be happy to help.
Note that as new PRs are merged into the master branch, a preview PDF is available at <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/releases/download/auto-pdf-preview/VOTable-draft.pdf">https://github.com/ivoa-std/VOTable/releases/download/auto-pdf-preview/VOTable-draft.pdf</a> (also via the icon/badge at the top of the VOTable github repo README <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable#readme">https://github.com/ivoa-std/VOTable#readme</a>).
Known Open Issues
-------------------------
We're maintaining the list of known issues in Github. This is the complete list of known issues that could still be addressed in version 1.5: <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/issues?q=is%3Aopen+is%3Aissue+milestone%3Av1.5">https://github.com/ivoa-std/VOTable/issues?q=is%3Aopen+is%3Aissue+milestone%3Av1.5</a>
Of those, only 2 are "must do" so have a label of "Priority: High":
- Update sections 7.1 and 7.2 to match schema changes for COOSYS (<a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/issues/41">https://github.com/ivoa-std/VOTable/issues/41</a>)
- Update the change log - section 9.4 (Differences Between Versions 1.4 and 1.5, <a class="moz-txt-link-freetext" href="https://github.com/ivoa-std/VOTable/issues/46">https://github.com/ivoa-std/VOTable/issues/46</a>)
Please review this Working Draft at your earliest opportunity. I look forward to the discussion and suggestions on <a class="moz-txt-link-abbreviated" href="mailto:apps@ivoa.net">apps@ivoa.net</a> as well as concrete proposals in Pull Requests (or new Github issues).
Best regards,
Tom
</pre>
</blockquote>
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