Websphere Portal on Z/OS

1.3 Logical tiers

In these architectures, a tier is any component that participates in the actual application transaction. A Web server acting as a reverse proxy, a firewall, a switch or a router are not considered tiers. They are viewed as being part of the networking infrastructure.

Our view follows the J2EE application model with some variation. We have added a wireless client and a portlet takes the place of a servlet as shown in Figure 1-1 on page 5.

Figure 1-1: Tiers in the application model

Portlets are reusable software components, running inside a portal, that provide access to Web-based content, applications, and other resources. From a user's perspective, a portlet is a window on the portal's Web browser screen, that provides a specific service or displays certain information. For people familiar with servlets in the Java world, a portlet is a specialized servlet. Portlets will be the focus of the architecture diagrams that follow and are covered in more detail in Chapter 6, "Portlet development and deployment" on page 181.

• For the portal architecture, in the client tier there are no fat clients, only thin browser clients and wireless clients. It is possible to use Java applets in the client tier.

• The Web tier normally contains the Web server, presentation logic, and the controller functions handled by portlets. Note that a portlet is an extension of a servlet.

• The business logic tier will contain Enterprise Java Beans (EJBs).

• In the Enterprise Information System (EIS) tier you have backend applications, databases, and transaction systems.