OrdinalFactory throws Exception

Methods in lass OrdinalFactory throw Exception (i.e. generic highest-level unspecified Throwable). This can be changed to more specific exception object.

The only usage for these Exceptions I could find after brief investigation is in PolicyManager#call, where it checks in a most generic way whether table.update succeeded. At least we could separate RuntimeException from exceptions thrown because of inner logic failure: bad IDs in arguments, inconsistency in datastore etc...