EJB Accelerator Data Conversion
When you use a transparent persistence interface like JDO with an object database, there is no need for data conversion (or mapping) from tables to objects and back. Both the Enterprise Java Beans (EJBs) and the database use the same object model. This is illustrated in the diagram where it indicates that no data conversion is needed.
If you use a relational database as part of an EJB accelerator, there will be data conversion. The location of that data conversion will depend on the interface you use:
For more information on EJB accelerators and application servers, see When to Use EJB Accelerators with Java Application Servers.
More on the general topic: Using EJB Accelerators with Application Servers