Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology / Logistic Engineering
M. Jerkovic Resource-constrained project scheduling. Notation, classification and some of the recent developments. Literature survey, Report 99.3.LT.5154, Transport Technology, Logistic Engineering.
Scheduling is the allocation of resources over time to perfonn a collection of tasks. It is a decision-making process that has as a goal the optimization of one or more objectives subject to precedence constraints and resource constraints. Also, it is a collection of principles, models, techniques, and logical conclusions that provide insight into the scheduling function.
The vital elements in scheduling models are resources and tasks. The resources and tasks may take many forms. The tasks may be called "jobs" or "projects" or "assignments" and are composed of elementary parts called "activities" or "operations" and "delays". Each activity requires certain amounts of specified resources for a specified time called the "process time". The resources are in limited supply and also have elementary parts, called
"machines", "cells", "transport", and so on. The objectjes may also take many forms. One possible objective is the minimization of the completion time of the last task, and another is the minimization of the number of tasks completed after the committed due dates. In general, scheduling is the process of organizing, choosing, and timing resource usage to carry out all the activities necessary to produce the desired outputs at the desired times, while satisfying a large number of time and relationship constraints among the activities and the resources.
Scheduling decisions are generally subject to both precedence constraints and resource constraints. The resource-constrained project scheduling (RCPS) model contains both types of constraints that characterize scheduling decisions. The relation of this topic to other scheduling problems can therefore be interpreted in two ways. First, the resource-constrained project scheduling problem can be formulated by adding explicit resource requirements and resource capacities to the basic network model of CPM (Critical Path Method) and PERT (Program Evaluation and Review
Technique). CPM and PERT have been regarded as tools for planning and scheduling large, nonrepetitive projects. Alternatively, the problem can also be formulated by allowing general precedence structures in the job shop problem and replacing machines by machine groups, for parallelism. Thus, the resource-constrained project scheduling problem contains the job shop scheduling problem as a special case. So far, no classification scheme exists which is compatible with what is commonly accepted in machine scheduling. Also, a variety of symbols are used by project scheduling researchers in order to denote one and the same subject.
One purpose of this report is to provide a classification scheme, i.e. a description of the resource envirornnent (the machine environment in the job shop model), the activity characteristics (task characteristics in the job shop model), and the objective function (optimality criterion or performance measure in the job shop model), which is compatible with machine scheduling and which allows to classify the most important models dealt with so far. The second purpose of this report is to review some of the recent developments.
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