
encapsulates the business rules and provides boundaries around the applica
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tion. The Application Layer operates primarily as a liaison between the Small
Programs Layer and the User Interface Layer. By unifying elements of the
Small Programs Layer in a single environment, it helps establish the relation
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ship among the small programs and provides the framework that ties them
together. In other words, it is the integration layer.
The User Interface Layer is the part that the user sees on the screen when
the application is invoked. It is highly malleable in that a variety of user inter
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face styles can be used depending on the desired presentation.