In Part 1 and Part 2 we explained that between 1975-81, when the E/RM and RDM were introduced, there was no distinction between an informal conceptual and a formal logical level. In 1980, however, Codd defined a formal data model and in the later 80s the conceptual-logical-physical levels of representation emerged. If applied to the two models:
- Only the RDM satisfies the definition;
- The E/RM can be used at the conceptual level to model reality, the latter can be used to model data at the logical level (i.e., formalize conceptual models as logical models for database representation).
Consider the question "does data modeling slow down an application development process?". I will set aside the notion of "speeding up" application development by skipping altogether "data modeling" (whichever way it is meant), and focus on the response.
