Using the JPA tools, you can generate data definition language
files for creating database tables from entity beans that you create.
About this task
In
top-down mapping, you start with entity beans and
use them to create your database tables. You start from scratch with
the entity definitions and the object-relational mappings, and then
you derive database schemas from that data. If you use this approach,
you are most likely concerned with creating the architecture of your
object model and then writing your entity classes. These entity classes
eventually drive the creation of your database model. If you are using
a top-down mapping of the object model to the relational model, develop
the entity classes, and then use the JPA tools DDL generation capability
to create the database tables that are based on the entity classes.
The
process of mapping database tables top-down from entity beans requires
these steps: