Checkpoint

Where We've Been

• We must consider several issues when mapping an object view of the system to a relational database design. The early inclination is to create one-to-one mappings, but this approach usually results in too many tables.

• Most one-to-one class associations can be collapsed into one relational table. This might not be the case if the association is optional.

• Three common approaches to mapping inheritance to the relational model are available. One is to create a table for each class involved and a view for each subclass. Another is to collapse all of the attributes from the subclasses into a table matched to the superclass. The last is to take the attributes found in the superclass and duplicate them in each table for each of the subclasses.

• Aggregation and composition associations are mapped in the same way as simple associations.

• We have many options for identifying primary keys. A common approach that offers significant flexibility is to use surrogate, or programming, keys.

• A visual modeling tool is a must for any project team that is serious about building object-oriented systems. Such tools can generate code, as well as SQL DDL.

• The Rational Rose modeling tool can be customized to add additional flexibility to the DDL generation process.

• Stored procedures and triggers should be viewed as the ultimate screwdriver for fine-tuning the application. If they are commingled with the business logic, the application becomes more dependent on the product architecture choices.

• The Enterprise JavaBeans (EJB) specification and its support for container-managed persistence (CMP) will be used to handle the data translation and data access features for Remulak.

Where We're Going Next

In the next chapter we:

• Explore the needs of the infrastructure layers as a whole, and es tab lish layer communication mechanisms and an error-handling process.

• Review the identified classes and assess all attributes that have been defined to ensure completeness.

• Build a template for applying the layered code.

• Begin to generate code components from the class diagram.