NeXus groups

[Ray Osborn]

>
>> 
>> Does anyone knows if it's possible to have NXentry groups within a
>> NXentry group ?
>> 
>
>If NXentry groups is just one kind of VGroup then it is possible.
>
>Within IDL there exists a routine 'HDF_VG_INSERT' which allows
>the user adding VGroup or VData to an existing VGroup. 
>
>Since IDL/HDF is build on top of HDF, may be there is a similar
>function or routine in HDF.
>
>Ben-chin

It is, of course, allowed by HDF to place Vgroups within Vgroups and HDF
places no limitations on class names.  However, the NeXus standard requires
that NXentry groups are only at the top level of a NeXus file.  This is how
<http://www.neutron.anl.gov/NeXus/NeXus_structure.html#Layout> describes
what is contained within a NXentry group :

"All the data, including instrument and sample descriptions, which logically
make up a single scan or measurement. At many facilities, this corresponds
to the entity that is defined by a single run number, which could be used to
name the NXentry group. There can be many NXentry groups in each NeXus file"

Therefore, according to the standard, the answer is no.  There can be more
than one NXdata group within each NXentry if you want to include multiple
data sets as part of the same "scan" or "run".

Ray Osborn
-- 
Dr Ray Osborn                Tel: +1 (630) 252-9011
Materials Science Division   Fax: +1 (630) 252-7777
Argonne National Laboratory  E-mail: ROsborn at anl.gov
Argonne, IL 60439-4845