WebSphere Application Server - IBM Redbooks

► You may have more than one view of the same model. If both the business
logic and its presentation were built together, adding an additional view would
cause considerable disruptions and increase the component's complexity. A
good example of a model with two views would be a banking application that
can be accessed through both the Internet and mobile phones.
► You do not want to have to change the model every time you modify the view.
The view is definitely dependent on the model, since it presents specific
aspects of the model to the user. It makes no sense, however, to have the
model depend on the view. Building both together dramatically increases the
chances of this happening, and of you having to change the model every time
you implement a small change to the view.
This separation can be achieved through the layering of the component into:
► The model layer, responsible for implementing the business logic.
► The view layers, each responsible for rendering the user interface (be it
graphical or not) to a specific client type and in a specific fashion.
With these two layers, we can implement the business logic and present it to the
user. That solves only half of the problem. We would also like to be able to
interact with the model. The implementation of this interaction is better left to a
third layer, called controller.
This model-view-controller structure has several benefits:
► You can isolate development effort to some extent, so that implementation
changes in one part of the Web application do not require changes to another.
The developers responsible for writing the business logic can work
independently of the developers responsible for the flow of control, and
Web-page designers can work independently of the developers.
► You can more easily prototype your work. For example, you might:
– Create a prototype Web application that accesses several
workstation-based programs.
– Change the application in response to user feedback.
– Implement the production-level programs on the same or other platforms.
Outside of the work you do on the programs themselves, your only
adjustments are to configuration files or name-server content, not to other
source code.
► You can more easily migrate legacy programs, because the user interaction is
the same wherever those programs run and however they interact with data
stores.
► You can maintain an environment that comprises different technologies
across different locations.
Chapter 2. Application design 29