HDF tag query

Mark Koennecke koenneck at psi.ch
Wed Sep 1 09:00:32 BST 1999

On Wed, 25 Aug 1999, Freddie Akeroyd wrote:

> Hi ... i've recently been doing a bit more with the NeXus side of
> OpenGENIE, and i've come across something i don't quite understand.
> NXmakedata() adds an SDS to a Vgroup with the tag DFTAG_SDG (a "scientific
> data group"), but if you ask NXgetdataID() for the "tag,ref" pair it
> returns the tag DFTAG_SDS (a "scientific data scale"). Is this a trick so
> that you can distinguish the creation/initial reference of a data set (tag
> DFTAG_SDG) from any links to it (tag DFTAG_SDS)?  The only thing that
> concerns me is that the documentation says that a "ref" value is not
> unique unless bound to a "tag" value, so the object "DFTAG_SDS,ref" may
> not refer to a valid object in the file.  While this doesn't cause a
> problem with our code (we hunt for both DFTAG_SDS and DFTAG_SDG, and then
> assume the "ref" is really from DFTAG_SDG), could it cause a problem for


  you were right. I tested it and changed NXgetdataID to set the tag to
  DFTAG_SDG. Then the linked SDS's showed up nicely in the Fortner browser
  which they did not do before. It never occurred to me that DFTAG_SDS
  means scientfic data scale and scientific data set. Abbreviations! 

  In short I suggest to change that in the general distribution.

                  Mark Koennecke 

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