Context of an ERD

ERDs are used in many different ways. We've used them here as an aid in database modeling. They can be a first, high-level step to get an impression of what we are dealing with. We define the scope and create a rough first draft of what our database might look like.

Application developers who write queries against databases need to know the database. What information is stored where? An ERD is a handy tool to get the needed insight. You see all the tables and which tables are related. When you add keys to the ERD (name an entity as we did plus add the primary and foreign keys in the entity's rectangle), you also know how tables are related. You can even add all the columns, as in Figure 2.1 at the start of this chapter. This ERD contains all the detailed information needed to start implementing the database.

There are multiple steps to be taken in between what we have created so far and the ERD of Figure 2.1. In Chapter 3, Normalizing Data, we are...