Introduction to Life Cycle Processes
Generic Systems Engineering Paradigm
The term life cycle is one that engineering has borrowed from the natural sciences, where it is used to describe both the changes a single organism goes through over it life and how the lives of multiple organisms interact to sustain or evolve a population. We use it in the same way to describe the complete life of an instance of a system-of-interest (SoI); and the managed combination of multiple such instances to provide capabilities which provide stakeholder satisfaction.
Figure 1 identifies the overall goals of any SE effort, which are: the understanding of stakeholder value; the selection of a specific need to be addressed; the transformation of that need into a system (the product or service that provides for the need); and the use of that product or service to provide the stakeholder value. This paradigm has been developed according to the principles of the systems approach discussed in Part 2 and is used to establish a basis for the KAs in Part 3 and Part 4 of the SEBoK.
On the left side of Figure 1, there are SoI's identified in the formation of a system breakdown structure. SoI 1 is broken down into its basic elements, which in this case are systems as well (SoI 2 and SoI 3). These two systems are composed of system elements that are not refined any further.
On the right side of Figure 1, each SoI has a corresponding life cycle model which is composed of the stages that are populated with processes. The function of these processes is to define the work that is to be performed. Note that some of the requirements defined to meet the need are distributed in the early stages of the life cycle for SoI 1, while others are designated to the life cycles of SoI 2 or SoI 3. The decomposition of the system illustrates the fundamental concept of recursion as defined in the ISO/IEC 15288 standard; with the standard being reapplied for each SoI (ISO/IEC 15288). It is important to point out that the requirements may be allocated to different system elements, which may be integrated in different life cycle stages of any of the three SoI's; however, together they form a cohesive system. For example, SoI 1 may be a simple vehicle composed of a chassis, motor and controls, SoI 2 an embedded hardware system, and Sol 3 a software intensive interface and control system.
When performing SE processes in stages, iteration between stages is often required (e.g. in successive refinement of the definition of the system or in providing an update or upgrade of an existing system). The work performed in the processes and stages can be performed in a concurrent manner within the life cycle of any of the systems of interest and also among the multiple life cycles.
This paradigm provides a fundamental framework for understanding generic SE (seen in Part 3), as well as for the application of SE to the various types of systems described in Part 4.
Please provide your comments and feedback on the SEBoK below. You will need to log in to DISQUS using an existing account (e.g. Yahoo, Google, Facebook, Twitter, etc.) or create a DISQUS account. Simply type your comment in the text field below and DISQUS will guide you through the login or registration steps. Feedback will be archived and used for future updates to the SEBoK. If you provided a comment that is no longer listed, that comment has been adjudicated. You can view adjudication for comments submitted prior to SEBoK v. 1.0 at SEBoK Review and Adjudication. Later comments are addressed and changes are summarized in the Letter from the Editor and Acknowledgements and Release History.
If you would like to provide edits on this article, recommend new content, or make comments on the SEBoK as a whole, please see the SEBoK Sandbox.blog comments powered by Disqus