The Unified Modeling Language (UML) is a widely used, object-oriented design method, which provides a variety of diagrams for expressing different views or features of a software system [BRJ98] [Fow97].
UML object diagrams describe a software system in terms of a set of objects and their relationships or interactions. Normally, objects can be referred to within a UML object diagram in three ways:
The relations between objects in a UML object diagram are association (also known as use), aggregation and composition. Note that UML object diagrams are very similar to UML class diagrams, although object diagrams do not have the inheritance relation. [Fow97].
UML object diagrams are therefore made up from objects and their relationships, as the following example shows:
UML sequence diagrams describe the interactions among a group of software component with emphasis on the chronological ordering of messages.
In the version of UML sequence diagrams used in this book, simple message relations between objects (basic software components) are considered.
Objects or software components are presented as a square containing ...