RM versus entity-relationship diagram
Recall that an RM can be identified from business-relevant concepts and mapped onto a database schema that includes their attributes, identifiers, and relationships. An entity-relationship diagram (ERD) is a visual rendering of the RM using simple, easy-to-understand semantics.
In the following examples, we will revisit a set of relational entities from Chapter 1, Unlocking the Power of Modeling. In the RM, each of the three entities corresponds to a table identified by a primary key and related to other entities through foreign keys. Just observing the table names or even a data preview does not make it easy to determine these relationships, as can be seen in the following RM:
SUPERHERO --------- SUPERHERO_NAME|BIRTHPLACE   |SUPERHERO_TYPE|HAS_MASK| --------------+-------------+--------------+--------+ Ratman        |Gotham Gutter|Accident      |true ...
