UML Scope Specification

The UML has a more limited scope than people often assume. The OMG's Request for Proposal was primarily concerned with the development of a metamodel for OO modeling. The metamodel was expected to define an underlying language that could be transmitted between products that support visual modeling without constraining the vendors to a particular methodology for developing the models.

System development focuses on three different models of the system

1. The functional model, represented in UML with use case diagrams, describes the functionality of the system from the point of view of the user .
2. The object model, represented in UML with class diagrams, describes the structure of the system in terms of objects, attributes, associations, and operations. During requirements and analysis, the object model starts as the analysis object model and describes the application concepts relevant to the system. During system design, the object model is refined into the system design object model and includes descriptions of the subsystem interfaces. During object design, the object model is refined into the object design model and includes detailed descriptions of solution objects.
3. The dynamic model, represented in UML with interaction diagrams, state machine diagrams, and activity diagrams, describes the internal behavior of the system. Interaction diagrams describe behavior as a sequence of messages exchanged among a set of objects, whereas state machine diagrams describe behavior in terms of states of an individual object and the possible transitions between states. Activity diagrams describe behavior in terms control and data flows.

This metamodel defines the underlying meaning of each element used in visual modeling and the relationships among them. For example, in the UML metamodel, you will find a detailed description of a class; its component parts, attributes, and operations; and the relationships among them. You will not find a process for finding classes or for evaluating a "good" class specification versus a "bad" class specification. Nor does the metamodel define the visual icons used for each model element .

Nine diagrams are defined in the UML metamodel. Each is fully described in the metamodel using class diagrams and textual narrative. The net result for most of us is a set of standardized visual models that may be used with many different modeling processes. The process chosen may vary widely among industries, applications, and practitioners.
The key to the UML is understanding that you can use it with any number of different development methods, process controls, and quality measures. The rest of this course is devoted to explaining the purpose and definition of each UML diagram and their relationships to one another. This understanding should prepare you to apply the models in your own unique environment.
In the next lesson, how UML is being refined and extended to provide the most flexibility and applicability will be discussed.