The Logical Data Model (LDM) is derived from the Conceptual Data Model (CDM).
The CDM consists of the major entity sets and the relationship sets, and does not state anything about the attributes of the entity sets.
The LDM consists of the Entity Sets, their attributes, the Relationship sets, the cardinality, type of replationship, etc.
The Physical Data Model (PDM) consists of the Entity Sets (Tables), their attributes (columns of tables), the Relationship sets (whose attributes are also mapped to columns of tables), along with the Datatype of the columns, the various integrity constraints, etc.
Erwin calls the conversion / transformation of LDM => PDM as Forward Engineering which further leads to the actual code generation and the conversion of Code => PDM => LDM as Reverse Engineering!
Though the question says specifically about Erwin, the above explanation is independent of the datamodeling tool used for the purpose. |
