The logical three-tier model, as shown in the following figure, has a user interface that is physically separate from another machine that contains the application logic and the data. Physically, all three logical tiers can also be hosted on a single machine. Therefore, physically there are only one or two machines, but technically, or logically, there are three tiers: the user interface, the application logic, and the data.
Figure 2. Logical three-tier model
The configuration of the logical three-tier model promotes the writing of business logic and deploying them on an application server close to the data. An OpenEdge implementation of this model has the AppServer or WebSpeed connect to the database server using shared memory; the need to access the database over the network has been eliminated, providing faster data access to the business logic that processes it.
Another important feature of this model is the fact that the AppServer or WebSpeed remotely processes the information and only returns the results to the user interface. This capability minimizes the number of network messages while it delivers the specific data you need.
