The primary fields are
the identifier fields. The primary fields are used to identify the
asset type exclusively.
The mandatory fields are
the fields that are required for data collection and evaluation.
Without the presence of the mandatory fields, the asset is not
imported into the asset system.
The optional fields are
the fields that are not required for asset import, data collection,
or evaluation. The new fields that you can add to the custom asset
type are optional fields. They have no reference to the entity