These are internal"abstract" Datatype which will translated at generation time or at displaytime to the choosen DBMS Datatype, when you are in a PDM, i a CDM they are they are the primary datatypes, thought.
see some tables as an example to understand the concept:
from MSQL to internal:
and Internal to Postgres:
A is Alpha and will translatet to CHar, Varchar or whatever TargetDB understands, MN is Money and will be traslated to Mony, or it TargetDB does not have Moneytype to decimal or somehow.
HTH