IBM
Contents Index Previous Next



Object Model Notation


The object model notation used in the SDL Suite is an adaptation of the notations used in OMT (Object Modeling Technique) and UML (Unified Modeling Language). The OMT/UML notation is a commonly accepted graphical notation that is used for drawing diagrams that describe objects and the relations between them.

Class

The most important concept in an object model is the class definition. A class is a description of a group of similar objects that share the properties defined by the class. The properties of a class are described with attributes and operations. The object model notation for a class is exemplified in Figure 7, where the second class definition also shows how to define attributes and operations.

Figure 7 : A collapsed class symbol and a class symbol
with attributes and operations

Classes may inherit attributes and operations from other classes, known as specialization and generalization. The object model notation for this is shown in Figure 8.

Figure 8 : inheritance between classes

Relations and Multiplicity

Classes may be physically or logically related to each other. This is shown in the object model by means of associations as shown in Figure 9. An association may have a name and/or the endpoints of the association may be labeled by the role of this endpoint.

Figure 9 : Associations between classes

Aggregation is special kind of association, indicating a "consists of" relation. It has its own notation as shown in Figure 10.

Figure 10 : Aggregation

The endpoints of associations and aggregations may have a multiplicity according to the following:

Objects

Besides class definitions, object models may also contain objects (instances) and their relations. The relation that exists between objects are links, which corresponds to associations for classes. The object symbol has one field containing the object name and a reference to the class ("name:class"), and an attribute field where constant or default values can be assigned to the object attributes. See Figure 11.

Figure 11 : Objects related by links


http://www.ibm.com/rational
Contents Index Previous Next