Skip to content

File References from Devices

Some devices create their own files instead of sending their data to BEC. These are most often large area detectors with their own backend for writing HDF5 files.

BEC supports this by letting devices report file information through ophyd-side helper signals such as FileEventSignal in ophyd_devices.utils.bec_signals. Devices can also indicate hinted entries in their files that the master file should link to. This allows the master file to link to specific datasets in the external file instead of linking to the file root.

Learn about BEC signal classes

How DefaultFormat uses file references

DefaultFormat.write_bec_entries() creates /entry/collection/file_references.

File references from all devices are collected in that group as external links. For each hinted entry, DefaultFormat creates an external link with the hinted name. If there are no hints, it creates a fallback link named data that points to the root of the external file.

That means custom file-writer plugins can reuse the collected references through self.file_references and place additional external links wherever their NeXuS layout needs them.

When this matters for custom formats

This mechanism is useful when:

  • a detector writes its own HDF5 file
  • the master file should link to detector data instead of duplicating it
  • a beamline-specific layout wants links under entry/instrument/... or entry/data

In those cases, the custom writer can use self.file_references together with create_ext_link(...) to place links in the desired structure.