ABSTRACT
Our goal in this chapter is to explain the second phase of CWA, control task analysis, in
full detail.1 As we explained in chapter 3, control task analysis and work domain analysis
are complementary. Although an analysis of control tasks does not identify the support
required to deal with unanticipated events, it does allow us to identify the requirements
associated with known, recurring classes of situations. Such an analysis can identify the
constraints on what needs to be done, independently of how or by whom. We describe the
decision ladder (Rasmussen, 1974, 1976), a modeling tool that can be used to develop
control task models. An example of how the decision ladder can be used to conduct a
control task analysis is presented for the DURESS II process control case study
introduced in chapter 6. By the end of this chapter, you should understand how control
task constraints both inherit, and build on, the work domain constraints discussed in the
previous chapter.
