N-tier model is a computing model for implementing application partitioning. It supports flexible network structuring so that you can distribute application logic and the processing load among many machines across your distributed network. Because the n-tier model can support an unlimited number of clients, application servers and data sources, you can break up monolithic applications and flexibly reconfigure them to run in a network environment that best supports your computing needs.
The n-tier model supports the logical separation of user interface, application logic, and data access across two or more machines. Because of this flexibility, application partitioning in a distributed environment is closely tied to two basic deployment approaches:
The logical three-tier model
The physical n-tier model
The logical three-tier model supports separating the application logic from the user interface in the application implementation, and moving it to a remote server where the application data resides. A configuration based on the logical three-tier model can remain a physical client/server application in that it is deployed across two machines. However, the user interface, application logic, and data are logically separated from one another because the application logic owns access to all the data. In contrast, the physical n-tier model supports both logically and physically discrete segments. Each segment-user interface, application logic, and data—can be deployed on separate machines across the enterprise even with widely-separated resources in each segment (as over a WAN).
In an OpenEdge distributed environment, you are not restricted to using just these models, and these models can co-exist in a distributed environment. This chapter presents these models as a means to understand the various capabilities available in the OpenEdge distributed environment.
The logical three-tier model