Persistent Java Objects in 3 Tier Architectures

The 3 tier architecture logically separates the functions of an application into a user interface component, a server business logic component, and a database component. Many application server products, ORBs, and middleware products provide support for building and deploying applications using the 3 tier architecture. In most of these cases a primary role of the middle tier business logic components is to manipulate data stored in and accessed from the 3 rd tier. The GemStone/J application server includes a capability for creating, storing, and using persistent Java objects in the middle tier. We argue that the use of persistent Java objects in the middle tier of a 3 tier application offers significant advantages over other approaches. The standard 3-tier architecture consists of presentation and application logic in the client, application and business logic in a middle tier application server, and data managed by database servers in the 3 rd tier. The application is typically controlled by user interface in the client with substantial application processing taking place in the middle tier application server. The middle tier code typically drives 3 rd tier data queries, updates, and transactions and implements shared business logic. Data manipulation performed by the application is typically done on object representations of 3 rd tier data fetched through queries, or through data manipulation APIs or SQL code that operates in the database server. There may be some small amount of configuration data used to govern activities in the middle tier, but usually it is stored in specialized files designed for specific configuration and management purposes. Customer service application for an electric utility-Employees answer phone calls from customers who are reporting problems with electric service. The user interface displays customer account and location information so a trouble ticket can be generated that contains information about the nearest lines, transformers, etc.. The application server accumulates and dispatches trouble tickets as well as caching customer account and system information from a 3rd tier mainframe database.