STC version 1.3(0) posted

[Arnold Rots]

I have posted the revised document and schema for STC, version 1.30,
on ivoa.net.

This version has been expanded over the draft version 1.30, but is
fully backward compatible.

Currently, it is being used in VOEvent, the registry, and the Johns
Hopkins footprint service.
I have appended a list of the most significant changes since the
previous version.

  - Arnold

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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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The most significant changes from version 1.21:

    * A new referencing mechanism, Xlink, that is robust and flexible; in case of ambiguities, the precedence is:
         1. Content of the element
         2. Content of element referred to by IDREF attribute
         3. Content referenced by Xlink attributes
         4. UNKNOWN
      Any element that is either missing or which content cannot be determined is assumed to be UNKNOWN, in which case it is up to the client to either reject the document or choose a suitable default.
    * Replacing Lists of doubles (i.e., arrays, particularly in multi-dimensional - spatial - coordinate axes) by explicit enumeration of the individual components.
    * Allowing units to be specified at all levels of coordinates (i.e., also at the leaves).
    * Simplified version of error circles in 2-D and 3-D
    * Name optional in Coordinate elements, Timescale optional in astronTimeType
    * Rename Region Shape "Constraint" to "Halfspace".
    * Add "Difference" to Region operations (redundant but practical).
    * Optional epoch attribute; precedence:
         1. Epoch provided in coordinate leaf element
         2. Epoch provided in higher coordinate node
         3. Time of observation
         4. Equinox of, or implied by, coordinate system
         5. UNKNOWN
      Note that under most circumstances, where an observing time is provided, epoch is not needed.
    * Allow position to be specified by orbital elements.
    * Allow definition of a position path (curve).
    * Removed all anonymous types.
    * Added application-specific types (in particular for footprint service).
    * Consolidated everything in one schema.
    * Added basic support for generic coordinates.
    * Added an optional UCD attribute to the basic STC attribute group.
    * Revised inheritance structure: Pixel and Astro versions of CoordSystem, Coords, and CoordArea now derive from the generic ones by extension, and thus include the generic versions as well.
    * Coordinate transformations are now fully supported through the CoordRefFrame mechanism.