1Introduction

1.1 Introduction to Sequencing and Scheduling

Scheduling is a term in our everyday vocabulary, although we may not always have a good definition of it in mind. Actually, it’s not scheduling that is a common concept in our everyday life; rather it is schedules. A schedule is a tangible plan or document, such as a bus schedule or a class schedule. A schedule usually tells us when things are supposed to happen; it shows us a plan for the timing of certain activities and answers the question, “If all goes well, when will a particular event take place?” Suppose we are interested in when dinner will be served or when a bus will depart. In these instances, the event we are interested in is the completion of a particular activity, such as preparing dinner, or the start of a particular activity such as a bus trip. Answers to the “when” question usually come to us with information about timing. Dinner is scheduled to be served at 6:00 p.m., the bus is scheduled to depart at 8:00 a.m., and so on. However, an equally useful answer might be in terms of sequence rather than timing: That is, dinner will be served as soon as the main course is baked, or the bus will depart right after cleaning and maintenance are finished. Thus, the “when” question can be answered by timing or by sequence information obtained from the schedule.

If we take into account that some events are unpredictable, then changes may occur in a schedule. Thus, we may say that the bus leaves at 8:00 a.m. unless ...

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