Unformatted text preview: Even today it is not always used because of the effort required to set up a scheduling system to do the resource leveling. For smaller projects or under certain conditions, simple scheduling may still be appropriate. We discuss resource leveling in Section 7.2.3. During the mid-1960s, most companies that used any form of scheduling charts, including PERT charts, developed their own computer programs if they wanted automated assistance with computing schedules. At Texas Instruments, in 1968, the author produced what we believed to be the first scheduling program that automatically drew precedence-diagramed PERT charts on a plotter while automatically minimizing the number of lines that intersected. There may have been earlier programs that drew arrow-diagramed charts, but at the time we were unable to locate any such computer program described in the literature. Simple scheduling is characterized by the defining of the expected duration for each task to the scheduling system (in addition to the dependency types and lag times already mentioned in the previous section). The scheduling system then Page 182 performs two types of algorithms, known as the forward pass algorithm and the backward pass algorithm, to produce the schedule. What is obtained in this process is two different sets of dates for each task. The first set of dates is known as the early date set , and the second set of dates is known as the late date set . The early date set consists of the early start date and the early finish date. The late date set consists of the late start date and the late finish date. The early dates are the earliest possible dates that a task can start and finish based on the dependencies and lag times specified to the scheduling system. Of course, it is possible for the task to start later and finish later. The question is: How much later can they start and finish without causing the overall project to finish late? The answer is the late dates. The late start date is the latest date the task can start without jeopardizing the project schedule, and the late finish date is the latest date the task can finish without causing the project to finish behind schedule. There are many papers and books that the interested reader can refer to that describe these algorithms in detail. Their presentation is far beyond the scope of this book. What we are interested in here is how the durations are estimated. Even if simple scheduling is to be used on a project, the estimate of the duration of a task should not be made until the budgeting of the task has been completed . Without an understanding of the man-hour budget for the task, it is difficult, if not impossible, to determine how long it will take to accomplish the task. Sometimes it is possible to determine the duration of many of the tasks in a straightforward manner, but more often it is a complex, time-consuming job, because the estimate of the duration of a task depends not only on the amount of work to accomplish (man-hours to complete) but the conditions under which the work can be undertaken. For instance, workers may not be allowed to work on weekends in order t...
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This note was uploaded on 01/11/2011 for the course ACC 9 taught by Professor Yeetan during the Spring '10 term at Sunway University College.
- Spring '10