topcat TAP client enhancements

[Mark Taylor]

Dear DAL,

this is a short report of a couple of DAL-relevant changes in the
TAP client of the recent topcat release (v4.3-4).  I present them
here for service providers who might like to modify their services
to take advantage of them.

  - Column index: topcat now honours the (TAP 1.1) "column_index"
    column from the TAP_SCHEMA.columns table to decide what
    order to display column metadata in.  That can make the metadata
    significantly more readable for users, so I encourage services
    to add that column if they can.
    Services don't need to declare themselves as TAP 1.1 for
    topcat to use this column.

  - Non-standard table/column metadata: if the TAP_SCHEMA.tables
    or TAP_SCHEMA.columns tables contain non-standard columns,
    their values will now be presented in the TOPCAT GUI.
    That gives TAP services the chance to add useful items like
    table row count, column statistics etc and have them visible
    in the GUI.  See Gregory Mantelet's ARI-Gaia service for a
    nice example of this in action.  To transmit the corresponding
    information when the /tables endpoint is used instead for
    acquiring service metadata, XML attributes in a private
    namespace can be used (again, see ARI-Gaia for examples).

  - VOSI 1.1: topcat now has a TAP service metadata acquisition
    mode that can use the ?detail=max/min parameter proposed
    for VOSI 1.1.  This is not used by default, but can be
    turned on with the TAP|Metadata Acquisition menu item.
    If services want to implement this behaviour, I'd be
    interested to test them.  It would be a good idea to make
    this the default mode for querying TAP metadata in future,
    since the service gets some say over how much metadata is
    downloaded at one time.  I may do that in the future if
    it works well with available services (it should do because
    of backward compatibility of the protocol for services that
    are properly VOSI1.0 compliant, but currently not all are)

Mark

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/