The available tools and support for building planning and scheduling systems and applications have been steadily improving for decades. At the same time, the scope, scale, and complexity of the problems to be addressed has been increasing. In this column, I discuss several different scheduling applications developed over the past 25 years, and then describe the tools and techniques used in addressing these problems, showing how improved tools simplified (and in some cases enabled) the solution of problems of increasing difficulty.

Neither of these terms are fundamental categories. The initial AIMS scheduling problem encompassed 29,000 discrete activities, subject to 97,000 complex metric constraints specified by AIMS applications developers. Generating feasible schedules was an essential requirement for operating the 777, potentially threatening a Boeing investment of almost 10 billion dollars. The scale and complexity of this problem were unprecedented, and there were very few applicable tools or standards. Input requirements were provided as text, with a semantics negotiated and maintained through frequent discussion.