[From IBM DeveloperWorks
Application Servers (also called App Servers) are gaining popularity as a way to provide information and services to people at different locations without regard to the type of computer they are using. Typically the App Server sits between a database or other information store (called the backend) and an end-user / customer (called the client) creating what is termed a "three-tier architecture." This article discusses setting up IBM Cloudscape or Derby as the backend for a system using an Application Server that is compliant with Sun's Java Enterprise Edition (J2EE) specification. In the configuration described here, the database management system (DBMS) may also be referred to by the term Resource Manager.
The article continues at http://www.ibm.com/developerworks/db2/library/techarticle/dm-0509bradbury/index.html