Extended Entity-Relationship Model to tables (subclasses)

Question

In the EER model there are subclasses entities. I was wondering what's the way to implement that in a real SQL Table or if there is any guide that might help me out to understand how to implement entities subclasses into tables that would help. Thanks

Answer 1

Martin Fowler's book Patterns of Enterprise Application Architecture covers solutions for subclassing tables:

• Single Table Inheritance
• Class Table Inheritance
• Concrete Table Inheritance

These correspond to the options in the answer from @spencer7593, without being tied to Java & Hibernate.

Answer 2

The Hibernate documentation has discussion of the options available for representing inheritance hierarchies in a relational database. There are undoubtedly better tutorials, but the Hibernate ORM (love-it-or-hate-it) wrestled with this problem.

Because there is no single "best way" to represent an inheritance hierarchy, they support all the options:

• table per class hierarchy - basically one table, with all the attributes from all the subclasses. lots of columns will likely be null on lots of rows

• table per subclass - one table for the superclass, and a separate table for each subclass

• table per concrete subclass - separate table for each subclass (no table for superclass)

There's no single right answer. Each of these approaches benefits and drawbacks.

http://docs.jboss.org/hibernate/orm/3.3/reference/en-US/html/inheritance.html