The last few chapters have introduced the concepts of analysis and design, along with various modelling techniques appropriate to these activities. We have also discussed some general topics, such as ensuring that your models are readable, that they are produced iteratively and incrementally to better accommodate change both in their requirements and in your own understanding of these requirements. In this chapter we will be discussing some general design guidelines which you may want to keep in mind when designing software systems. We will break these down into general areas such as abstraction and architecture, each dealt with in their own section.