TABLE OF CONTENTS The concept of time is a critical element in systems engineering. It leads directly to the subject of change, and in particular, raises the following question: How do we adequately address change in systems engineeringff This chapter discusses concepts of time, types of change, and especially levels of change. A running theme is the application of change models from biology.
Previous chapters, especially Chapter 7, have discussed the concept of similarities and differences. In this chapter we look at the temporal aspects of these concepts. One way to think about this chapter is that the time dimension of the model space is a temporal specialization of similarities and differences. We think of similarity across time as stability, and differences or variability across time as change. A bridge between the two is that invariants represent what is common and stable, and variants represent what differs and changes. If everything were stable, then time could be abstracted away, and we would not need to include this chapter, or the time dimension in the model space. However, change is ubiquitous; that is, it is everywhere and it is continual in the natural world and the engineering world. Therefore, change is the aspect of time that motivates and dominates this chapter.
We believe that traditional systems engineering (TSE) has not given sufficient attention to temporal change in systems engineering (SE) processes and in the assumptions about engineered systems and their environments. As D rner...
