Ray asked:

   1) HDF doesn't allow you to specify the tag when you call SDcreate.  It just
   assigns one for you.  It seems to be assigning DFTAG_SDG, which HDF claims
   not to support any more.

The code in $(HDF4.1r2-ROOT)/mfhdf/libsrc/mfsd.c:1015::SDcreate() is 

#ifdef NOT_YET
    var->ndg_ref = Htagnewref(handle->hdf_file,DFTAG_NDG);
#else /* NOT_YET */
    var->ndg_ref = Hnewref(handle->hdf_file);
#endif /* NOT_YET */

and NOT_YET is not yet defined. So, they are clearly planning to move
to DFTAG_NDG, but haven't done it at least until 4.1r2, where it just
returns the next available ref.  Could people survey their versions
and find out if it was put in eventually. Ray, what is your version of
HDF?

   2) If we then use the wrong tag to attach the SDS to a particular Vgroup,
   why do we encounter no problems?  We always assume that the tag is DFTAG_NDG
   even though it's not.

   It doesn't seem to affect the operation of the NeXus file, but I'm worried
   that it might have hidden side effects if we don't sort it out.   Perhaps it
   explains why data items still do not show up when linked to more than one
   group.  Does anyone know how we are meant to set the SDS tag?  Am I missing
   something here?

Hmm, I don't know. If we are looking for the wrong tag, it won't be there.
I agree that we should sort it out because it looks like something to
bite us in the future.

			przemek klosowski, Ph.D. <przemek@nist.gov>  (301) 975-6249
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