[NeXus-tech] file with multiple entry groups, each with multiple data groups

[Pete Jemian]

A question came up this morning [#context]_ regarding NXsample and how 
to store data from an "experiment".  As used, an "experiment" might 
involve many samples and other forms of variety such as multiple 
instrumental techniques.  One use case cited was for an experiment 
involving many samples, another use case was a tomography data set with 
many images acquired, another use case was the SAXS/WAXS technique.  The 
documentation with the NXentry base class mentions a "measurement" 
without defining that word.

Some years ago, the canSAS documented a standard XML representation for 
1-D reduced small-angle scattering data [#1]_.  Several example data 
files were presented [#2]_.

One of the example files is relevant to the discussion as it contains 
data for an "experiment" involving many related samples.  Each sample is 
regarded as a measurement which contains one or more data sets.  A brief 
description is provided [#3]_, with a link to the complete experiment 
provided in a single XML file.  The data is for an aging study of the 
AF1410 steel alloy, the study of which is published [#4]_.

It is possible to access this data online, directly from the canSAS 
repository, as shown in some example Python code [#5]_.

The design of the canSAS 1d/1.1 standard uses groups and fields derived 
from the contemporary NeXus standard.  It should be relatively easy to 
discern the general file structure, admitting that the SASdata group 
internal structure looks a bit different than NeXus.

I assert the AF1410 XML file describes data that satisfies today's use 
of "experiment", as well as the word "measurement" as used in the 
NXentry documentation.  There are other ways to represent this data as 
well, using NeXus base classes similar to the canSAS classes and 
possibly multiple files.  The choices for the AF1410 are based on the 
particulars of the data.

The AF1410 data (and other canSAS example files) will be transcoded into 
NeXus once the NXcanSAS definition is ready.

Pete


.. [#context] in the context of a discussion of the draft NXcanSAS 
application definition and specifically about NXsubentry
.. [#1] http://www.cansas.org/formats/canSAS1d/1.1/doc/index.html
.. [#2] 
http://www.cansas.org/formats/canSAS1d/1.1/doc/examples.html#other-example-data-files
.. [#3] 
http://www.cansas.org/formats/canSAS1d/1.1/doc/casestudy_af1410.html?highlight=af1410
.. [#4] Acta Metall 41 (1993) 1869-1884
.. [#5] http://pyresttable.readthedocs.org/en/latest/examples/cansas.html