CREATING THE LOGICAL MODEL - A Developer's Guide to Data Modeling for SQL Server - page 168

F IGURE 7.7

The entities for Mountain View Music, with primary keys and relationships

added

the case of applications that can generate physical models from the logical
model, may result in incorrect schema.

Domains
Now that our model has entities, primary keys, and relationships, it's a good
time to review the domains we're using. In truth, this is a review phase that
will help facilitate the addition of the full list of attributes for each entity.
But it also serves to facilitate the process of adding the attributes.
As described in earlier chapters, domains are definitions of attributes
that are universal to the model. For example, the system may require that
all employee identification numbers (EINs) be nine digits long, regardless
of leading zeros. Thus, we have chosen to model this using the char data
type, which will have a length of nine characters. The EIN may be an at-