[netCDF #GFI-182980]: NetCDF-4 and multiple links to a data object

Hi Mattia,

> My name is Mattia Pedergnana and I am currently working at the German
> Aerospace Agency in Munich. I went through the NetCDF-4 library and I would
> like to kindly ask you if it possible to create different variables which
> point to the same data object. If not, do you think there is any technical
> issue (within the NetCDF-4 standard) by using the HDF5 library to create
> them?
> 
> Library: NetCDF-4 version 4.2.1.1
> System: Linux Suse 12.2

One of the HDF5 features omitted, to keep the netCDF enhanced data
model simple, was HDF5 References.  Other omitted features for which
there is no netCDF-4 support are listed here:

  http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#fv15

So if you create an HDF5 file that uses HDF5 References, you can't
access them from the netCDF-4 API.  You may still be able to read the
data, if there is a standard variable pointing to it, but I don't know
whether the netCDF-4 library just ignores other object References, or
whether the presence of References in the file causes problems
accessing the data by other means.  If you find out by trying it, I'd
be interested in the result.

Although the netCDF-4 library provides no support, it may be possible
to implement some of the functionality of references using attribute
conventions.  For example, a variable attribute named "reference_to"
could name a different variable in the file, so that any scalar
variable it was attached to could serve as an alias for a different
variable.  However, that convention would have to be supported by
software that implemented the desired semantics, or by modifications
to the library.

The other kind of HDF5 references, pointing to a region of data
elsewhere in the file, adds enough extra complexity that it would
probably be better just to use HDF5, if that's what you need.  It's
not our intention to make netCDF-4 a complete replacement for HDF5.
NetCDF-4 is just trying to fill the niche of simpler than HDF5 but not
as powerful, to provide a trade-off that's better for some users ...

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: GFI-182980
Department: Support netCDF
Priority: Normal
Status: Closed