Since the first implimentation of DAGMC for MCNP-X there has been a need to define problem metadata; such as which volumes are assgined to be steel at a specific density, which volumes are to be water, in which volumes we would like to determine neutron flux and so on. For earlier version of DAG-MCNP5 an ad-hoc schema was defined which would associate any volumes with a material property and if specified specific tallies. This method was limited to MCNP5/X and supported only a subset of the potential geometric metadata.
CNERG have developed a new scheme known as “The University of Wisconsin Unified Workflow” - (UW\(^2\)), with this scheme we encode problem metadata as raw text strings which are interpreted downstream by a pre-process tool. Material assignments are specified with the mat:<name> key-value pair. This data is stored in the geometry file and is indelibly associated with the volume. The PyNE \cite{pyne2014,Bates2014} MaterialLibrary capabillity is used to look up the association of that material name to the composition as defined in the material library. This PyNE Material object, is then inserted into the geometry file thus a local copy of that which was present and permenantly inserted into the geometry file. This material object is then used at run time to translate the PyNE form into the physics engine specific form.
Similarly for material metadata, there exists methods to handle the tally specific metadata, for this purpose a specific class was written for PyNE which allows the instanciation of tallies with names, volume id numbers and so on. The syntax for the creation of tallies is tally: particle name \ tally type , using the naming PyNE particle naming scheme. Like with Materials, the Tally objects are stored in the geometry file and translated to physics engine specific form at run time.
Currently Cubit is used to assign this metadata using the group feature, where volumes which have a consistent property are assigned to the same group. The group data are handled by a pre-process code which assigns each volume in the group the property belonging to the group. Ultimately, as input every DAGMC enabled code is capable of recieving an identical description of material compositions and identical descriptions of tallies.