If you want to take advantage of using an ODBMS in the middle tier and have one or more existing relational databases, you will need to map data from a relational format to an object format.
So, if you need to map, consider using an object-relational mapping product. They will save you time and reduce the number of defects in your mapping. For more information on object-relational mapping products, click here.
An object-relational mapping product is shown at the left of this figure. It handles the mapping and has a cache much like an ODBMS. Data is mapped to the ODBMS and from the ODBMS based on the application needs. The ODBMS provides high-speed performance for the Internet.
For more information on mapping details, see mapping.
For how to use object-relational mapping with Java application servers, see enterprise architectures using Java application servers.
More on the general topic: Architecture with Existing Data Sources