DR2XML key features

Dr2xml is a Python package for translating the CMIP6 Data Request to XIOS file_def XML files. It also produces complementary field_def and axis_def XML files [-not yet available-]; these will complement hand-written XML files: the native field_def of the model and what we call, in dr2xml jargon, the “ping file”.

Dr2xml generates one file_def XML file per XIOS context (i.e. per realm or group of realms). That file_def sets the file structure and name in conformance with the Data Reference Syntax (DRS, see the WIP position paper: https://drive.google.com/file/d/0B-X2uY_FGt7XNWI2TzBsUXdCVkE/view ), includes the global attributes (metadata about the experiment, the model, the producing laboratory, etc.) and local attributes (metadata about the output CMOR variables) imposed by CMOR. Temporal and spatial operations consistent with the specified DR cell_methods, to be performed on the instantaneous and global variables of the native field_def, are automatically coded by dr2xml with appropriate XIOS filters in a complementary field_def [-not yet available-], possibly referring to complementary axis_def [-not yet available-].

Complementary field_def files aggregate XIOS temporal and spatial operations required to produce CMOR Variables from model outputs (for e.g.: axis reduction to compute zonal means, temporal averages for global indices computation).

The ping file establishes the correspondence between model variable names listed in the native model field_def and the variables names referenced in the file_def produced by dr2xml (dr2xml being agnostic of the native model variable names, this ping file represents the interface between model and dr2xml). Given the long list of variables requested by the DR, a tool, provided along with dr2xml sources, enables to generate a template for an exhaustive ping file. The “only” modeller work is to scan each line of this skeleton and associate (when it exists) a native model variable name to each of the expected output variable. This work is to be done once for all, once the Data Request is stabilized (see section 4 for details).

Dr2xml also offers two functionalities allowing the user to deviate/modulate the variable list that comes from the official Data Request, giving the possibility to the user to define:

  • a list of excluded variables: among the DR variables list, these ones will be excluded from the resulting file_def (because they do not apply to the model or for any good reason the modeller decide not to output them); an alternate way to exclude variables is through ping file syntax (see section 4 - not yet implemented)

  • a list of home variables: a list of variables that the lab intends to produce in some case. This covers both purely “home” variables (i.e. which have no CMOR equivalent), and CMOR Variables that are not requested by the DR for this MIP/experiment but the lab decides to output anyway; these ones will be added in the file_def.

Excluded-variables usage is described in section 2; home-variables list functionality is described in section 3.