8.1 Introduction

This chapter looks at how the UML can be extended using three basic extension mechanisms: stereotypes, constraintsand tagged values. In order to illustrate these concepts an example will be considered, that of modelling websites. There are two main reasons for this: almost everyone is familiar with the world-wide web nowadays and very few people have modelled this using the UML, so it represents an interesting new application area.

Before the first example models are introduced, a rough background to the rationale behind modelling websites will be discussed. Once the scene has been set for the modelling, some examples will be introduced.

The first examples will be concerned with defining and applying stereotypes to UML elements for a particular example, in this case websites. This example is then taken further by adding constraints to the existing models in order to add new rules to the UML. The final type of extension mechanism, tagged values, shows how extra information may be added to UML models that may help with outside tasks, such as project management and version control.

The concepts discussed in this chapter have already appeared at various points throughout the book and the reader is encouraged to revisit these models after reading this chapter.

8.2 Modelling websites