As part of my work on DM-3372 (“stack provenance”), I added a new feature to the CameraMapper that allows us to provide a default specification for datasets. This allows us to add datasets that will be defined in the same way for all cameras. This meant that I didn’t have to add a packages dataset in all the obs_* packages (to save the package version information), but by putting it in a single place it takes effect for all the obs_* packages. Beyond that convenience, I hope it will also allow us to simplify the existing obs_* packages by moving most of the coadd products into a single place.
The default dataset specifications are stored in daf_butlerUtils/policy as images.yaml, exposures.yaml, calibrations.yaml and datasets.yaml, according to which category of dataset it is. They have the same information as what would go in our *Mapper.paf files, but (as the file extensions suggest) are in YAML. Files that don’t currently exist are treated as empty.