[Nexus-developers] NXconvert-NXtranslate

[Ray Osborn]

On 11/20/03 10:46, "Mark Koennecke" <Mark.Koennecke at psi.ch> wrote:

> I still seem not to get it: The NXtranslate-XML file is a recipe for
> converting files. It produces a NeXus file. If this NeXus file is to
> be filled with live data later or a SDS is to be rpelaced by live data,
> this must be indicated somehow (This is still undefined). Please give a
> more detailed usage scenario (who calls NXtranslate, when and where is
> the live data taken from, etc.)

Here's the scenario.  The data acquisition system is set up so that, when a
run starts, all the metadata concerning the run is placed into a standard
conforming NeXus file, either XML or binary.  However, the data tags are
left empty but the NXtranslate attributes, which point to the library that
reads data from electronic memory, are added instead.

When a data analysis program wants to access the data, there are two
approaches.

1) Run the translation utility to convert the file to a regular NeXus file
with the NXtranslate attributes replaced by real data.

2) In the longer term, add a thin GetData layer to the NeXus API so that
external libraries can, optionally, be linked through it to the API.  Data
analysis programs, on the instrument computer, would link to NeXus API
containing this external data interface, so that a NXgetdata call would use
the NXtranslate attributes to get the external data directly.

With the second scenario, the same data analysis programs can work both on
regular NeXus files and on files where the data is external.  All that would
be necessary would be to link to the external library.  In some systems,
this linking could even be done dynamically at run time.

When the data are archived, the data tags are filled with real data and the
NXtranslate attributes are removed.

For the time being, we would probably use option 1, but the architecture
would allow us to migrate to option 2 when we are ready.

By the way, Peter is going to be unavailable for a week or so, so I will try
and represent his views for the time being.

Best regards,
Ray
-- 
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