Managing & Using MySQL, 2nd Edition

Data Model

A data model is a diagram of our database design. It documents and communicates how the database is structured.

Notice that we capture several pieces of data (CD title, band name, etc.) about each CD, and we absolutely cannot describe a CD without those items. CD is therefore one of those things we want to capture data about and is likely to be an entity. To start a data model, we will diagram CD as an entity. Figure 7-1 shows our sole entity as a data model.

Figure 7-1. The CD entity in a data model

By common entity naming conventions, an entity name must be singular. We therefore call the table where we store CDs CD and not CDs. We use this convention because each entity names an instance. For example, “San Francisco 49ers” is an instance of “Football Team,” not “Football Teams.”

At first glance, it appears that the rest of the database describes a CD. This would seem to indicate that they are attributes of CD. Figure 7-2 adds them to the CD entity in Figure 7-1. In a data model, attributes appear as names listed in their entity’s box.

Figure 7-2. The CD entity with its attributes

This diagram is simple, but we are not done yet. In fact, we have only just begun. Earlier, we discussed how the purpose of data modeling is to eliminate redundancy using a technique called normalization. ...