Building Distributed
Applications
Using the Progress AppServer
Progress Distributed Application Computing Models
In contrast, Progress distributed application computing, through the introduction of the Progress AppServer, expands computing capabilities beyond the limited boundaries of the two-tier model. This section discusses two models: the logical three-tier model and the n-tier model. As previously mentioned in this chapter, these models help illustrate how you can distribute your application in a Progress distributed environment. You are not limited to using just these models.
The Logical Three-Tier Model
The logical three-tier model, as shown in Figure 1–2, has a user interface that is physically separate from another machine that contains the application logic and the data. Therefore, physically there are only two machines, but technically, or logically, there are three tiers: the user interface, the application logic, and the data.
Figure 1–2: Logical Three-tier Model
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The configuration of the logical three-tier model promotes building business rules and deploying them in an environment close to where the data resides. A Progress implementation of this model enables the Application Server to connect to the database server using shared memory; the need to access information over the network has been eliminated, providing faster data access.
Another important feature of this model is the fact that the Application Server remotely processes your information, and only returns the results to you; this capability minimizes the number of network messages while it delivers the specific data you need.
The N-tier Model
In addition to the logical three-tier model, the Progress distributed environment supports an n-tier configuration. Although this model does not capitalize on the use of shared memory, and introduces an additional network connection that you do not have in the logical three-tier model, the deployment flexibility of this model might have significant benefits from an overall enterprise perspective. Figure 1–3 shows how application logic can be distributed to dedicated machines without any local database connections.
Figure 1–3: N-tier Model
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For example, you might want to configure a Progress AppServer on a system that is a dedicated computation engine with no locally attached database. With the Progress AppServer, you can build arbitrary complex applications across any number of computing tiers, based on the business problem that you are trying to solve.
The remaining chapters in this manual help you understand the Progress AppServer and how you can design and implement it as an integral part of your distributed application computing environment, beginning with Overview of the Progress AppServer."
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