TABLE OF CONTENTS This section introduces use case diagrams, which realise a behavioural aspect of the model. The behavioural view has an emphasis on functionality, rather than the control and logical timing of the system. The use case diagram represents the highest level of abstraction of a view that is available in the UML and it is used, primarily, to model requirements and contexts of a system. Use cases are covered in greater depth in Chapter 7 and thus this section is kept deliberately short, emphasising, as it does, the structure of the diagrams.
Use case diagrams are arguably the easiest diagram to get wrong in the UML. There are a number of reasons for this:
The diagrams themselves look very simple, so simple in fact that they are often viewed as being a waste of time.
It is very easy to go into too much detail on a use case model and to accidentally start analysis or design, rather than very high-level requirements and context modelling.
Use case diagrams are very easy to confuse with data flow diagrams as they are often perceived as being similar. This is because the symbols look the same since both use cases (in use case diagrams) and processes (in a data flow diagram) are represented by ellipses. In addition, both use cases and processes can be decomposed into lower-level elements.
Information on the practical use of use cases is surprisingly sparse, bearing in mind that many approaches that are advocated...
