7.1 Introduction

At this point, it wouldn't be surprising if you are wondering the following:

• Why the topic has been left until now (when we've already used diagrams extensively)?
• If you are faced with learning the details of yet another set of diagrams?

Dealing with the first point: diagrams were introduced – in a very informal way – only as and when needed (in other words, used in a relevant context). The reasons for doing this are threefold. First, it demonstrated the power of diagramming techniques. Second, it implicitly made a good case for using diagrams as a design tool (they aren't just a set of pretty pictures). Third, it (hopefully) made the task of learning the syntax and semantics of a wide range of diagrams a fairly painless process. Now, though, we can deal with diagramming in a more formal manner. And, to answer the second question: yes, we will meet some new diagrams along the way. But we won't need to redo the material...