Model-View-Controller (MVC) Design Pattern

Model View Controller design pattern is used to support multiple types of users with multiple types of interfaces. The Model-View-Controller (MVC) pattern separates the modeling of the domain, the presentation, and the actions based on user input into three separate classes:

- Model: The model locates all data information for the application. It does not care about how you interpret it or how process it. It divides functionality among objects involved in maintaining and presenting data to minimize the degree of coupling between the objects.

- View: The view manages the display of information. It is responsible for maintaining the consistency in its presentation when the underlying model changes.

- Controller: The controller interprets the mouse and keyboard inputs from the user, informing the model and/or the view to change as appropriate. The actions performed on the model can be activating device, business process or changing the state of a model.

The MVC pattern allows any number of controllers to modify the same model. The strategies by which MVC can be implemented are as follows:
- For Web-based clients such as browsers, use Java Server Pages (JSP) to render the view, Servlet as the controller, and Enterprise JavaBeans (EJB) components as the model.
- For Centralized controller, a main servlet is used to make control more manageable.

The System Engineering Hierarchy - System Modeling

Good system engineering begins with a clear understanding of context - the world view - and then progressively narrows focus until technical details are understood. System engineering encompasses a collection of top-down and bottom-up methods to navigate the hierarchy.
System engineering process begins with a world of view which is refined to focus more fully on a specific domain of interest. Within a specific domain, the need for targeted system elements is analyzed. Finally, the analysis, design, and construction of targeted system element is initiated. Broad context is established at the top of the hierarchy and at the bottom, detailed technical activities are conducted. It is important for a system engineer narrows the focus of work as one moves downward in the hierarchy.

System modeling is an important element of system engineering process. System engineering model accomplishes the following:
- define processes.
- represent behavior of the process.
- define both exogenous and endogenous input to model.
- represent all linkages.

Some restraining factors that are considered to construct a system model are:
- Assumptions that reduce number of possible permutations and variations thus enabling a model to reflect the problem in a reasonable manner.
- Simplifications that enable the model to be created in a timely manner.
- Limitations that help to bound the system.
- Constraints that will guide the manner in which the model is created and the approach taken when the model is implemented.
- Preferences that indicate the preferred architecture for all data, functions , and technology.
The resultant system model may call for a completely automated or semi automated or a non automated solution.