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Developing Applications with Java™ and UML by Paul R. Reed

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Logical versus Physical Tiers

The three services layers are often called tiers, or in this case, three logical tiers. They might be separated by well-defined interfaces, thereby allowing for less troublesome changes in the future, but they are considered logical because they may be implemented on only two physical tiers. Figure 8-2 depicts the notion of logical versus physical tiers.

Figure 8-2. Logical versus physical tiers

This very common implementation scheme represents a logical three-tiered solution that is actually implemented on two physical tiers: the client and server. Called fat-client or client-centric, this solution initially served ...

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