UML diagrams

The UML includes specifications for nine different diagrams used to document four different views Use case view, Logical view, Component view, Deployment view) of a software solution from project inception to installation and maintenance. The specifications define the elements of each model, how the models are assembled, and how they can be extended.

The use case view employs the use case model to capture user requirements. The use case view contains only one model, the use case model. The goal of the model is to identify the functionality required by users before trying to model a solution. The model uses a diagram, a narrative description of the diagram, and scenarios to model these requirements.

Five modeling elements make up the use case diagram: system, actors, use cases, associations, and dependencies. ach association becomes a dialog that must be explained in a use case narrative. Each narrative in turn provides a set of scenarios that function as test cases when evaluating the design and implementation of the use case.

The system notation is a rectangle with a name. In use case diagrams, people, systems, and devices are all referred to as actors. An actor is a role that an external entity plays in relation to the system. Use cases define the required features of the system and notation is an oval with name in it. Without these features, the system cannot be used successfully.

A line connecting an actor to a use case represents an association. The UML specification however states that an association is simply a line to show that there is communication between the two elements. These connections will form the basis for the interfaces of the system and subsequent modeling efforts. Sometimes one use case may need to ask for help from another use case. When one use case delegates to another, the association is drawn as a dashed arrow from the "including" use case to the "included" use case and labeled with the <> stereotype notation.

The logical view uses class and object diagrams, sequence and collaboration diagrams, activity diagrams, and state chart diagrams to capture the conceptual design of the software solution. The logical view is by far the most inclusive of the views. It contains six models - Activity diagram, Class diagram, Object diagram, Sequence diagram, Collaboration diagram, and State chart diagram. These diagrams are designed to model every aspect of a software solution, each diagram providing its own specialized portion of the total specification for a system.

The component view use a corresponding diagram to model the physical implementation of the solution. The component view shows the physical arrangement of finished pieces of software. The view contains only one model, the component diagram. The component diagram may be used for a variety of purposes. It can be used to illustrate subsystems, applications, programs, or databases.

The deployment view each use a corresponding diagram to model the physical implementation of the solution. The deployment view addresses the need to map software to hardware. Typically, very different people and organizations manage these two environments, and there is no easy way to model their relationships. The deployment diagram allows the developer to represent the hardware environment in a notation very similar to that used for classes. Hardware is described in terms of features, functionality, and connectivity. Software components, described using the component diagram, are then superimposed on the deployment diagram to map the relationships between the two directly.

UML also provides packages. Packages are not a modeling tool. Packages are an organizational tool. Packages allow you to organize or group the UML modeling diagrams into logical units.

What is UML?
UML Diagrams
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