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Design and realisation of a knowledge base

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par Sawssan SELMI
 - Ingénieur en informatique 2011
  

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Fig17. Model-view-controller

Participants & Responsibilities

It was originally applied to map the traditional input, processing, and output tasks to the graphical user interaction model. Thus, it is straightforward to map these concepts into the domain of multi-tier enterprise applications.

§ Model - The model represents data and business rules that govern access to and updates of this data. Often the model serves as a software approximation to a real-world process, so simple real-world modeling techniques apply when defining the model.

§ View -The view renders the contents of a model. It accesses enterprise data through the model and specifies how that data should be presented. It is the view's responsibility to maintain consistency in its presentation when the model changes. This can be achieved by using a push model, where the view registers itself with the model for change notifications, or a pull model, where the view is responsible for calling the model when it needs to retrieve the most current data.

§ Controller - The controller translates interactions with the view into actions to be performed by the model. In a stand-alone GUI client, user interactions could be button clicks or menu selections, whereas in a Web application, they appear as GET and POST HTTP requests. The actions performed by the model include activating business processes or changing the state of the model. Based on the user interactions and the outcome of the model actions, the controller responds by selecting an appropriate view.

Strategies

Web-based clients such as browsers. Java Server Pages (JSP) pages to render the view, Servlet as the controller, and Enterprise JavaBeans (EJB) components as the model.

Centralized controller. Instead of having multiple servlets as controllers, a main Servlet is used to make control more manageable.

3.3.1.2. DAO

We use a Data Access Object (DAO) to abstract and encapsulate all access to the data source. The DAO manages the connection with the data source to obtain and store data.

The DAO implements the access mechanism required to work with the data source. The data source could be a persistent store like an DBMS. The business component that relies on the DAO uses the simpler interface exposed by the DAO for its clients. The DAO completely hides the data source implementation details from its clients. Because the interface exposed by the DAO to clients does not change when the underlying data source implementation changes, this pattern allows the DAO to adapt to different storage schemas without affecting its clients or business components. Essentially, the DAO acts as an adapter between the component and the data source.

Structure: Figure18 shows the class diagram representing the relationships for the DAO pattern.

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