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