Learning PostgreSQL 11 - Third Edition

Mapping ER to relations

The rules to map an ER diagram to a set of relations (that is, the database schema) are almost straightforward, but not rigid. One could model an entity as an attribute, and then refine it to a relationship. An attribute that belongs to several entities can be promoted to be an independent entity. The most common rules are as follows (note that only basic rules have been covered, and the list is not exhaustive):

• Map regular entities to relations. If entities have composite attributes, then include all the subparts of the attributes. Pick one of the key attributes as a primary key.
• Map weak entities to relations. Include simple attributes and the subparts of the composite attributes. Add a foreign key to reference ...