Remove epoch propagation and cleanup for WD (#48)

* Remove COOSYS-based epoch propagation and update diff section * Add refposition attribute to COOSYS in section 7.2 * Note vocabularisation of COOSYS/@refposition in xsd * Change schema version to 1.5pre3 --------- Co-authored-by: Mark Taylor <[email protected]>
ivoa-std · Oct 22, 2023 · 9689d58 · 9689d58
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diff --git a/Makefile b/Makefile
@@ -71,7 +71,10 @@ STILTS ?= stilts
 test:
 	@$(STILTS) xsdvalidate \
 		schemaloc="http://www.ivoa.net/xml/VOTable/v1.3=VOTable.xsd" \
-		coosys_example.vot
+		timesys_example.vot
 	@$(STILTS) xsdvalidate \
 		schemaloc="http://www.ivoa.net/xml/VOTable/v1.3=VOTable.xsd" \
-		timesys_example.vot
+		stc_example1.vot
+	@$(STILTS) xsdvalidate \
+		schemaloc="http://www.ivoa.net/xml/VOTable/v1.3=VOTable.xsd" \
+		stc_example2.vot
diff --git a/VOTable.attr.tex b/VOTable.attr.tex
@@ -20,6 +20,7 @@
 		\attr{equinox}\\
 		\attr{epoch}\\
 		\attr{system}\\
+		\attr{refposition}\\
 	\hline\end{tabular}
 	\\ \\
 	\begin{tabular}{|l|}\hline
@@ -131,7 +132,7 @@
 \begin{tabular}{@{}c@{}}	%%% Start cell r2c2
 \begin{tabular}{|l|}\hline
 	\multicolumn{1}{|c|}{\elem{FIELDref}}\\
-	\multicolumn{1}{|c|}{{\em(\Aref{elem:FIELDref})}}\\ 
+	\multicolumn{1}{|c|}{{\em(\Aref{elem:FIELDref})}}\\
 	\hline{}
 	\requiredattr{ref}\\
 	\attr{ucd}\\
@@ -140,7 +141,7 @@
 \\ \\
 \begin{tabular}{|l|}\hline
 	\multicolumn{1}{|c|}{\elem{PARAMref}}\\
-	\multicolumn{1}{|c|}{{\em(\Aref{elem:PARAMref})}}\\ 
+	\multicolumn{1}{|c|}{{\em(\Aref{elem:PARAMref})}}\\
 	\hline{}
 	\requiredattr{ref}\\
 	\attr{ucd}\\

diff --git a/VOTable.tex b/VOTable.tex
@@ -678,12 +678,9 @@ \subsection{\elem{COOSYS} Element}
 has the following attributes, all of them (syntactically) optional:
 
 \begin{description}
-\item[\attr{ID}] Required if the \elem{COOSYS} element is to
-be referred to via the \attr{ref} attribute of the position components.
-This version of VOTable still recommends that practice, but in the
-future we intend to drop \attr{ref}-based back-references from
-components to \elem{COOSYS} in favour of \elem{FIELDref} and
-\elem{PARAMref} children (see below).
+\item[\attr{ID}] Required if the \elem{COOSYS} element has to
+be referred to via the \attr{ref} attribute of the position components,
+which is generally the case.
 
 \item[\attr{system}] Specifies the reference frame of the coordinates.
 The value must be taken from the IVOA \emph{refframe} vocabulary
@@ -725,7 +722,7 @@ \subsection{\elem{COOSYS} Element}
 specifications in Julian or Besselian years.
 
 \item[\attr{refposition}] The reference position for which the positions
-are given.  The values of this attribute should be taken form the IVOA
+are given.  The values of this attribute should be taken from the IVOA
 \emph{refposition} vocabulary (\url{http://www.ivoa.net/rdf/refposition}).
 At the time or writing, this vocabulary includes the terms
 % GENERATED: !vocterms refposition
@@ -738,58 +735,13 @@ \subsection{\elem{COOSYS} Element}
 % /GENERATED
 \end{description}
 
-To facilitate comparing data at different epochs (epoch propagation),
-since VOTable version 1.5, the \elem{COOSYS} element SHOULD also be used
-to group and label coordinates and their derivatives.  This is done by
-referencing the participating \elem{FIELD}-s and/or \elem{PARAM}-s from
-the element content using \elem{FIELDref} or \elem{PARAMref} with
-\attr{utype} attributes identifying the roles of the respective items.
-
-We define role names in terms of labels within the Coords data model
-\citep{2022ivoa.specQ1004R} where possible, using an ad-hoc prefix
-\verb|votable|:
-
-\begin{description}
-\item[votable:LonLatPoint-lon] The longitude (e.g., a Right Ascension).
-\item[votable:LonLatPoint-lat] The latitude (e.g., a Declination).
-\item[votable:ProperMotion-lon] The time derivative of the longitude in
-the tangential plane (``multiplied with $\cos(\delta)$'').  We currently
-define no way to annotate raw proper motions in longitude, which are
-very rare in modern catalogues.
-\item [votable:ProperMotion-lat] The time derivative of the latitude.
-\item[votable:LonLatPoint-dist] The radial coordinate.  Both parallaxes
-(when the unit of the referenced element is an angle) and actual
-distances (with length units) are admitted.
-\item[votable:ProperMotion-rv] The radial velocity.
-\end{description}
-
-None of these roles are mandatatory, but of course even rudimentary
-epoch propagation requires a full position and both proper motions.
-More roles (e.g., for errors) may be defined in the future.  VOTable
-readers therefore MUST accept VOTables with unknown COOSYS roles, though
-they MAY issue warnings for them.
-
-Note that there can be multiple \elem{COOSYS} elements per table.  An
-example would be when both equatorial and galactic coordinates are
-given, or when there are multiple reductions of the same underlying
-data.
-
 Also note that \elem{COOSYS} may be deprecated in the
 future in favor of a more generic way of describing the conventions used
 to define the positions of the objects studied in the enclosed tables.
 
 A \elem{COOSYS} element referenced via a \attr{ref} attribute
 SHOULD appear before the element that references it.
 
-Here is an example of a \elem{COOSYS} describing a series of position
-determinations and mean proper motions, while radial information is
-missing:
-
-\begingroup\small
-\verbatiminput{coosys_example.vot}
-\endgroup
-
-
 \subsection{\elem{TIMESYS} Element}
 \label{elem:TIMESYS}
 
@@ -894,9 +846,9 @@ \subsection{\elem{RESOURCE} Element}
 \elem{RESOURCE} qualified by \attrval{type}{meta} can be used e.g. to host
 MIVOT (Model Instances in VOTables) annotations \citep{2023ivoa.spec.0620M}.
 MIVOT defines a syntax to map VOTable
-data to any model serizalized in VO-DML \citep{2018ivoa.spec.0910L}. 
-It operates as a bridge between models and data that associates VOTable 
-metadata to data model leaves. 
+data to any model serizalized in VO-DML \citep{2018ivoa.spec.0910L}.
+It operates as a bridge between models and data that associates VOTable
+metadata to data model leaves.
 It also brings up data or metadata that were possibly missing in the actual dataset.
 MIVOT annotations have their own namespace; they have no impact on the VOTable schema.
 
@@ -2337,13 +2289,22 @@ \subsection{Differences Between Versions 1.3 and 1.4}
 
 \subsection{Differences Between Versions 1.4 and 1.5}
 \label{diff1.4-1.5}
+The differences between version 1.5 of VOTable and the preceding
+version 1.4 are:
 
 \begin{itemize}
-\item COOSYS now has a refposition attribute analogous to TIMESYS; it
-also admits FIELDref and PARAMref children now for building propagatable
-positions, and it is no longer derived from xs:string.  The latter means
-that you cannot have text content in COOSYS any more, which probably
-only was possible by accident and never had a meaning.
+\item COOSYS now has a \attr{refposition} attribute analogous to TIMESYS.
+\item The frame identifiers (\attr{system} attribute) in COOSYS are now taken
+from the refframe IVOA vocabulary.
+\item Clarifications and rewording on:
+  \begin{itemize}
+    \item the meaning of \elem{MIN} and \elem{MAX} \attr{value} attributes for
+    array types.
+    \item removing the recommendation to use xmlns to do utype prefix binding.
+    \item timescales for calendar epochs.
+    \item positioning advice for \attr{ID} and corresponding references.
+    \item noting that \elem{RESOURCE} elements can contain \elem{MIVOT} blocks.
+  \end{itemize}
 \end{itemize}
 
 % NOTE: IVOA recommendations must be cited from docrepo.bib

diff --git a/VOTable.xsd b/VOTable.xsd
@@ -23,14 +23,15 @@
 .Version 1.4wd-a: TD: updates for initial draft of v1.4.
 .Version 1.4: TD: Change version to 1.4
 .Version 1.5pre1: MD: adding refposition attribute and FIELDref/PARAMref
-  in COOSYS, which no longer is derived from xs:string, either.
-.Version 1.5pre2: MD: vocabularising frame attribute in COOSYS
+   in COOSYS, which no longer is derived from xs:string, either.
+.Version 1.5pre2: MD: vocabularising system attribute in COOSYS
+.Version 1.5pre3: TD: Undo the FIELDref/PARAMref addition to COOSYS
 -->
 <xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"
    xmlns="http://www.ivoa.net/xml/VOTable/v1.3"
    targetNamespace="http://www.ivoa.net/xml/VOTable/v1.3"
-   version="1.5pre1"
+   version="1.5pre3"
 >
 <xs:annotation><xs:documentation>
     VOTable is meant to serialize tabular documents in the
@@ -225,25 +226,29 @@
 
 <!-- Expresses the coordinate system we are using -->
 <xs:complexType name="CoordinateSystem">
-  <xs:sequence minOccurs="0" maxOccurs="unbounded">
-    <xs:choice>
-      <xs:element name="FIELDref" type="FieldRef"/>
-      <xs:element name="PARAMref" type="ParamRef"/>
-    </xs:choice>
-  </xs:sequence>
-
-  <xs:attribute name="ID" type="xs:ID" use="required"/>
-  <xs:attribute name="equinox" type="astroYear"/>
-  <xs:attribute name="epoch" type="astroYear"/>
-
-  <xs:attribute name="system" default="FK5">
-    <xs:annotation>
-      <xs:documentation>
-        Values for this attribute must be taken from the IVOA
-        refframe vocabulary, http://www.ivoa.net/rdf/refframe
-      </xs:documentation>
-    </xs:annotation>
-  </xs:attribute>
+  <xs:simpleContent>
+     <xs:extension base="xs:string">
+       <xs:attribute name="ID" type="xs:ID" use="required"/>
+       <xs:attribute name="equinox" type="astroYear"/>
+       <xs:attribute name="epoch" type="astroYear"/>
+       <xs:attribute name="system" default="FK5">
+         <xs:annotation>
+           <xs:documentation>
+             Values for this attribute must be taken from the IVOA
+             refframe vocabulary, http://www.ivoa.net/rdf/refframe
+           </xs:documentation>
+         </xs:annotation>
+       </xs:attribute>
+       <xs:attribute name="refposition" type="xs:token">
+         <xs:annotation>
+           <xs:documentation>
+             The reference position SHOULD be taken from the IVOA
+             refposition vocabulary (http://www.ivoa.net/rdf/refposition).
+           </xs:documentation>
+         </xs:annotation>
+       </xs:attribute>
+     </xs:extension>
+   </xs:simpleContent>
 </xs:complexType>
 
 <xs:simpleType name="Timeorigin">

diff --git a/coosys_example.vot b/coosys_example.vot
diff --git a/timesys_example.vot b/timesys_example.vot
@@ -1,6 +1,6 @@
 <VOTABLE version="1.5" xmlns="http://www.ivoa.net/xml/VOTable/v1.3">
   <RESOURCE>
-    <COOSYS ID="system" epoch="J2015.5" system="ICRS"/>
+    <COOSYS ID="system" epoch="J2015.5" system="ICRS" refposition="BARYCENTER"/>
     <TIMESYS ID="time_frame" refposition="BARYCENTER" timeorigin="2455197.5" timescale="TCB"/>
     <TABLE name="ts_data">
       <FIELD datatype="double" name="obs_time" ucd="time.epoch" unit="d" ref="time_frame"/>