This chapter has introduced, at a high level, the world of systems engineering. There were a number of key concepts that were introduced that were classified into four main groupings: projects, processes, systems and life cycles. It has shown how there are three evils that affect us all, which are complexity, a lack of understanding and communication issues. One way to address these three issues is to apply modelling. In order to model effectively, it is essential to choose a common modelling language that can be used by all relevant people. In order to choose an appropriate modelling language there are certain requirements that must be satisfied in that the modelling language must present a number of modelling options, be able to represent information at different levels of abstraction, have strong connection to reality and be able to represent the system from different points of view. The modelling language that will be described in this book is the systems engineering modelling language, or SysML, which is a visual modelling language, based on the UML that satisfies all the above-mentioned requirements. The remainder of this book looks in detail at the language itself and then explores some common uses and applications for modelling.

Modelling is fundamental to everything that is presented in this book. So far. a brief introduction to modelling has been discussed, along with a set of requirements for any modelling language. In order to produce any sort of real model it is essential that the model be looked at in terms of two aspects the structure and the behaviour. This chapter looks at both structural and behavioural modelling in turn and not only introduces the SysML syntax but, more importantly, introduces the main concepts that must be understood in order to model effectively.

SysML has introduced some very useful new elements and diagrams not present in the original UML. namely flow ports, flow specifications and parametric constraints. This chapter looks at these concepts in greater detail and discusses how the connectivity between parts of a system can be modelled, how parametrics can be used to constrain system behaviour and to help with validation of requirements.Modelling a system in terms of the blocks that make up the system does not give a complete structural representation of the system. What is also needed as part of the structural aspect of the model is a set of diagrams that shows how those blocks are connected. This can be done in SysML using flow ports and standard ports.

This chapter is concerned with modelling requirements. Requirements engineering is the discipline of engineering that is concerned with capturing, analysing and modelling requirements.The emphasis in this chapter is on how to use the SysML to visualize requirements rather than to preach about requirements engineering itself; this section is therefore kept as brief as possible, while covering the basics. The basic concepts that are covered here will all be addressed practically in subsequent sections with respect to the SysML.

While SysML has undoubtedly introduced some useful new notation and concepts in particular flow ports, flow specifications and parametric constraints it is not a new language but rather a subset of UML with some additions. The diagrams omitted from SysML may prove problematical for systems engineers wishing fully to model a system, particularly those working with software engineers who may be modelling with the UML and therefore using the omitted diagrams. One solution for systems engineers is to use UML rather than SysML. but to add SysML constructs to UML.