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Metadata

LEGEND metadata is stored in YAML or JSON. Formatting guidelines:

  • In general, field names should be interpretable as valid variable names in common programming languages (e.g. use underscores (_) instead of dashes (-))
  • Snake casing is preferred, i.e. separating non-capitalized words with underscores (_).

Physical units

Physical units should be specified as part of a field name by adding _in_<units> at the end. For example:

radius_in_mm: 11,
temperature_in_K: 7

Specifying metadata validity in time (and system)

LEGEND adopts the YAML format to specify the validity of metadata (for example a data production configuration that varies in time or according to the data taking mode).

A validity.yaml file is essentially a collection of records. Each record is formatted as follows:

- valid_from: TIMESTAMP
  category: DATATYPE
  mode: MODE
  apply:
  - FILE1.yaml
  - FILE2.yaml
  - ...

where:

  • TIMESTAMP is a LEGEND-style timestamp yyymmddThhmmssZ (in UTC time), also used to label data cycles, specifying the start of validity
  • DATATYPE is the data type (all, phy, cal, lar, etc.) to which the metadata applies. If omitted, it should default to all.
  • MODE can be reset, append, remove, replace. If omitted and this is the first record in the file, defaults to reset, otherwise defaults to append.
  • apply takes an array of metadata files, to be comined into the main metadata object depending on mode (see below). In general, the files are combined "in cascade" (precedence order first to last) into the final metadata object.

The above example record, if appearing at the top of the validity file, translates to:

Combine FILE1, FILE2 etc. into a single metadata object. Fields in FILE2 override fields in FILE1. This metadata applies only to DATATYPE data and is valid from TIMESTAMP on.

Modes:

  • reset: remove all entries from the existing metadata file list before applying (in cascade) the ones listed in apply.
  • append: append (in cascade) files listed in apply to the current file list.
  • remove: remove the file(s) listed in apply from the current file list.
  • replace: replace, in the current fule list, the first file listed in apply with the second one.