Chapter 18. Entities and Relationships
“The pure and simple truth is rarely pure and never simple.”
This chapter presents a more complex system and introduces a model diagram and its representation in tables.
Sam’s system started off with a simple setup—a Customer table and a CD table. The CD table had an entry for each physical CD. This corresponded to Sam’s paper system, in which each CD had a separate index card that recorded its being rented. The table looked like this.
Entities and Relationships
A system is often more complex than Sam’s example. There are more entities than just a CD, and there are relationships ...