[Nexus] deleting data

[Przemek Klosowski]

   Is it really a matter of philosophy? 
   Or is there some technical limitation as well?

   Because, on philosophy grounds, I would argue that some types of data might be 
   only of temporary interest. In my case, the question comes from using 
   attributes to tag data internally (I asked about this in a recent email to 
   the list). But I can think of other applications:  metadata that may change 
   with analysis, or data linked from NXdata groups to construct a default plot 
   that is refined on a later stage of the data processing,...

   The workaround of creating a new file is non-practical: what if you are 
   dealing with a huge file (e.g. a tomography experiment) in which you want to 
   delete a single attribute?

A good approach in this case would be to create new NXdata sections
and link the original data objects to avoid duplication, while
creating the new and changed sections. This requires some careful data
layout design, so that the changeable attributes can be separated from
the object that is being linked, but this makes sense anyway. A nice
complete NeXus file could start with NXdata containing the raw data
taken as-is from the instrument, with subsequent NXdata sections
containing sequential data reduction and refinement intermediate
results, concluded by data plots and perhaps the NXdata with the LaTeX
source for the resulting publication :)