OracleAS TopLink Architectures Overview

OracleAS TopLink is designed to work in both Java and J2EE applications. Since it was first introduced, the flexibility of OracleAS TopLink has led to its use in many architectural styles. This section introduces the five most common architectures associated with OracleAS TopLink. Although this section describes the architectures in relation to J2EE, OracleAS TopLink continues to fully support non-J2EE and Java applications as well.

For more information about the flexible architecture support of OracleAS TopLink, see Chapter 2, "OracleAS TopLink Architectures".

Three-Tier Application

The three-tier (or J2EE Web) application is one of the most common OracleAS TopLink architectures. This architecture is characterized by a server-hosted environment in which the business logic, persistent entities, and the OracleAS TopLink Foundation Library all exist in a single Java Virtual Machine (JVM).

The most common example of this architecture is a simple three-tier application in which the client browser accesses the application through servlets, Java Server Pages (JSPs) and HTML. The presentation layer communicates with OracleAS TopLink through other Java classes in the same JVM, to provide the necessary persistence logic. This architecture supports multiple servers in a clustered environment, but there is no separation across JVMs from the presentation layer and the code that invokes the persistence logic against the persistent entities using OracleAS TopLink.

EJB Session Bean Facade

A popular variation on the three-tier application involves wrapping the business logic, including the OracleAS TopLink access, in EJB session beans. This architecture provides a scalable deployment and includes integration with transaction services from the host application server. Communication from the presentation layer occurs through calls to the EJB session beans. This architecture separates the application into different tiers for the deployment.

The session bean architecture can persist either Java objects or EJB entity beans.

EJB Entity Beans with CMP

OracleAS TopLink provides CMP support for applications that require the use of EJB entity beans. This support is available on the leading application servers. OracleAS TopLink CMP support provides you with an EJB 1.1 and 2.1 CMP solution transparent to the application code, but still offers all the OracleAS TopLink runtime benefits.

Applications can access OracleAS TopLink-enabled EJB entity beans using CMP directly from the client, or from within a session bean layer. OracleAS TopLink also offers the ability to use regular Java objects in relationships with EJB entity beans.

EJB Entity Beans with BMP

Another option for using EJB entity beans is to leverage OracleAS TopLink BMP in the application. This architecture enables you to access the persistent data through the EJB API, but is platform independent.

The BMP approach is portable—that is, after you create an application, you can move it from one application server platform to another.

Two-Tier Application

A two-tier (or client-server) application is one in which the OracleAS TopLink application accesses the database directly. Although less common than the others architectures discussed here, OracleAS TopLink supports this architecture for smaller or embedded data processing applications.