Preface

Scheduling theory, born in the middle of the 1950s, has become an established area of operations research, with numerous widely quoted books and influential surveys that cover various stages of development in scheduling or addressing a particular range of its models. Journals are published, and regular conferences are held with scheduling as the main topic. Hundreds of researchers around the world work on further advancing this branch of knowledge, and thousands of students of all levels study its aspects either as a full course or as a part of more general courses related to operations research, operations management, industrial engineering, and logistics. As with most areas of operations research, scheduling is motivated by practical needs and its achievements are fed back into various areas of industry, service, transport, etc. Whatever the motivation or application, scheduling problems are normally formulated in terms of processing jobs on machines, with a purpose of optimizing a certain objective function. In classical deterministic machine scheduling, it is assumed that for a given job, its processing times on the machines are known and remain unchanged during the planning horizon. Although the classical scheduling models form a solid theoretical background, due to their too ideal nature, their immediate practical applications are very rare. It is not by chance that a major current trend of scheduling calls for studies of more realistic models that combine scheduling decisions with logistics decisions such as batching, transportation, and maintenance. The models of classical scheduling are too static and do not respond to possible changes of processing conditions. In reality, actual processing times of a job may be affected by the fact that either these conditions get worse, or they may improve, or undergo some changes which affect the processing time in a less predictable, not necessarily monotone way. One aspect addressed in this book is related to the study of such time-changing effects. The studies of scheduling problems with time-changing effects were originated by O.I. Melnikov and Y.M. Shafransky (both from Minsk, Belarus) in the late 1970s. By the mid-1990s, such studies had become a noticeable part of scheduling research, and currently, the total number of publications exceeds several thousands.