NeXus: a proposal for s common data exchange format for neutron scattering and x-ray instruments

M. Koennecke1, P. Klosowski2, J. Tischler 3, and R. Osborn4
1Paul Scherrer Institut, 2NIST, 3Oak Ridge National Laboratory, and 4Argonne National Laboratory

Currently each experimental facility in the neutron scattering ans synchrotron radiation field stores data in its own home grown data format. Mostly these are ASCII formats. This situation poses some problems for travelling scientists: they nedd to write data conversion utilities before they are able to evaluate their data. The plethora of file formats hinders reuse of specific data evaluation software developed elsewhere. And ASCII formats impose a large interpretation overhead for the large data sets collected nowadays with position sensitive detectors.

Therefore an international team of scientists set out to develop a data exchange format during several meetings. This new format is named NeXus.

NeXus has four levels: a physical file format, a structure for ordering data in the file, a glossary of common data item names and a set of application programmers interface functions (API) for interacting with NeXus.

As physical file format the hierarchical data format (HDF) developed by the National Center for Supercomputing Applications (NSCSA), USA was choosen. HDF is an efficient binary format which is portable across machine and operating system boundaries. HDF is also self describing and extendable.

The scheme for structuring information in a NeXus file and the glossary of common data item names will facilitate the writing of general data analysis programs.

The NeXus API protects the programmer from some of the idosyncrarcies of the HDF interface and facilitates reading and writing of NeXus files.

NeXus is now coming in operation as data format for the instruments at the new spallation source SINQ at PSI. Already the first NeXus aware data evaluation prograsm exist.

(posted 19-Nov-97 jw)