Clarification on DataLink service descriptor input parameters

[Damian, Adrian]

Hello DAL members,

I would like to bring to your attention an issue related to service descriptor input parameters in the DataLink (https://www.ivoa.net/documents/DataLink/20211115/WD-DataLink-1.1-20211115.html#tth_sEc4.3). The problem that I’ve run into relates to the fact that the syntax of `MIN` and `MAX` for those parameters is not explicit.

The example in that document (https://www.ivoa.net/documents/DataLink/20211115/WD-DataLink-1.1-20211115.html#tth_sEc4.7) as:



<PARAM arraysize="2" datatype="double" name="BAND"
           ucd="em.wl" unit="m" value=""
           xtype="interval">
      <DESCRIPTION>Spectral cutout interval</DESCRIPTION>
      <VALUES>
        <MIN value="3.52631986e-07"/>
        <MAX value="9.21500998e-07"/>
      </VALUES>
 </PARAM>

The VOTable parser in astropy does not like the syntax - it expects, and I would say logically so, that MIN and MAX have the type of the BAND param, i.e. an interval. Is there a reason not to have the above MIN and MAX expressed as the maximum interval, i.e. <MAX value="3.52631986e-07 9.21500998e-07”/>?


That would also be consistent with other types of PARAM. The CADC DataLink service, for example, also returns:

<PARAM name="CIRCLE" datatype="double" arraysize="3" ucd="obs.field" unit="deg" xtype="circle" value="">
        <VALUES>
          <MAX value="36.517259904944964 75.45304017944918 0.13160680194585758" />
        </VALUES>
 </PARAM>

which VOTable parser is happy with it.

Thank you,
Adrian









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