Mandatory metadata

Certain metadata contained in NeXus files are common to all DESY experiments, the mandatory metadata (MMD). The size of the MMD is small. But they are sufficient for a rough identification of the file contents. Besides, MMD are used by the ingestion procedure inserting files into the metadata catalogue.

Table 1.1: Mandatory metadata

NeXus field or attribute	ICAT field	Remark
/NXentry/experiment_identifier	Investigation	a unique beamtime IT
/NXentry/title	Investigation.Summary	description of the experiment
/NXentry/NXinstrument/name	Instrument.Fullname	name of the beamline
/NXentry/NXinstrument/name@short_name	Instrument.Name	short name of the beamline
/NXentry/NXinstrument/NXsource/name	Facility.Fullname	accelerator name
/NXentry/NXinstrument/NXsource/name@short_name	Facility.Name	short name for the accelerator
/NXentry/NXsample/name	Sample.Name	name of the sample
/NXentry/NXsample/chemical_formula	Sampletype.Molecularformula	the sample chemical formula
/NXentry/start_time	Instrument.Start_Date	start time of the scan
/NXentry/end_time	Instrument.End_Date	end time of the scan

Table 1.1 contains a list of the DESY MMD and it shows how the NeXus items are mapped to ICAT fields.

• /NXentry/experiment_identifier identifies the beamtime. Several NeXus files can have the same beamtimeId.
• /NXentry/title is supplied by the user. It is scan-specific.
• /NXentry/NXinstrument/name is the full beamline name, e.g.: HighRes Diffraction
• /NXentry/NXinstrument/name@short_name the name of the beamline, e.g. P08
• /NXentry/NXsample/name is the sample name, it is scan specific.
• /NXentry/NXsample/chemical_formula the chemical formula, it is scan specific, e.g. LaB4
• NXentry/start_time, NXentry/end_time start and end of a scan, expressed in ISO format, e.g. 2013-06-10T14:30:16.238875+0200.