subject: Explain the purpose of different types of objects identified during domain analysis. Explain how these objects interact among each other [print this page] Explain the purpose of different types of objects identified during domain analysis. Explain how these objects interact among each other
The different kinds of objects identified during domain analysis and their relationships are as follows:
Boundary objects: The boundary objects are those with which the actors interact. These include screens, menus, forms, dialogs, etc. The boundary objects are mainly responsible for user interaction. Therefore, they normally do not include any processing logic. However, they may be responsible for validating inputs, formatting, outputs, etc. The boundary objects were earlier being called as the interface objects. However, the term interface class is being used for Java, COM/DCOM, and UML with different meaning. A recommendation for the initial identification of the boundary classes is to define one boundary class per actor/use case pair.
Entity objects: These normally hold information such as data tables and files that need to outlive use case execution, e.g. Book, BookRegister, LibraryMember, etc. Many of the entity objects are "dumb servers". They are normally responsible for storing data, fetching data, and doing some fundamental kinds of operation that do not change often.
Controller objects: The controller objects coordinate the activities of a set of entity objects and interface with the boundary objects to provide the overall behavior of the system. The responsibilities assigned to a controller object are closely related to the realization of a specific use case. The controller objects effectively decouple the boundary and entity objects from one another making the system tolerant to changes of the user interface and processing logic. The controller objects embody most of the logic involved with the use case realization (this logic may change time to time). A typical interaction of a controller object with boundary and entity objects is shown in fig. 8.2. Normally, each use case is realized using one controller object. However, some use cases can be realized without using any controller object, i.e. through boundary and entity objects only. This is often true for use cases that achieve only some simple manipulation of the stored information.
