Sun Java Enterprise System 2005Q4 Technical Overview

Dimension 2: Logical Tiers

The interacting software components of distributed enterprise applications can be viewed as residing in a number of logical tiers. These tiers represent the logical and physical independence of software components, based on the nature of the services they provide.

The logical tier dimension of solution architecture is illustrated in the following figure.

Figure 2–4 Dimension 2: Logical Tiers for Distributed Enterprise Applications

Diagram showing four logical tiers, left to right: client tier,
presentation tier, business service tier, and data tier.

For the most part, logical tier architectures represent the distributed enterprise application layer of Figure 1–1 . The Java ES system service components discussed in Infrastructure Service Levels provide support to application components in all of the logical tiers shown in Figure 2–4. However, logical tier concepts also apply to system service components that provide application-level services, such as Messaging Server and Calendar Server.

Description of Logical Tiers

This section provides brief descriptions of the four logical tiers shown in Figure 2–4. The descriptions refer to application components implemented using the Java 2 Platform, Enterprise Edition (J2EETM platform) component model. However, other distributed component models, such as CORBA, also support this architecture.

Logical and Physical Independence

The architectural dimension illustrated in Figure 2–4 emphasizes the logical and physical independence of components, represented by four separate tiers. These tiers signify the partitioning of application logic across the various computers in a networked environment:

Tiered Architecture Applied to System Components

As shown in Figure 2–3, Java ES infrastructure service components provide the underlying infrastructure support for distributed software solutions. Some of these solutions, however, include application-level services provided directly by Java ES components. These solutions use logical tier design approaches.

For example, the email communication services provided by Messaging Server are implemented using a number of logically distinct configurations of Messaging Server. these distinct configurations each provide a distinct set of services. When designing messaging solutions, these distinct configurations are represented as separate components that are situated in different logical tiers, as shown in the following figure.

Figure 2–5 Messaging Server: Example of Tiered Architecture

Diagram showing Messaging Server components distributed among
the four logical tiers.

Note –

Figure 2–5 is not meant to be a complete logical architecture; a number of Java ES components are omitted to simplify the illustration. Lines connecting components represent interactions.

The logical separation of Messaging Server functions into different tiers allows the logically distinct configurations of Messaging Server to be deployed on different computers in a physical environment. The physical separation allows for flexibility in meeting quality of service requirements (see Dimension 3: Quality of Service). For example it provides for different availability solutions for the different instances, and different security implementations for different Messaging Server functions.