Fundamentals Of Project Management

A task can begin all tasks preceding it must be

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Unformatted text preview: assumption that unlimited resources are available. This yields the best-case solution. BASIC SCHEDULING COMPUTATIONS Scheduling computations in this section are based on the network in Figure 6-1. First, let us examine the node boxes in the schedule in Figure 6-2. Each contains the notations ES, LS, EF, LF, and DU. ES = Early Start LS = Late Start EF = Early Finish LF = Late Finish DU = Duration (of the task) Figure 6-1 CPM diagram for yard project. Forward Pass Computations Consider a single activity in the network, such as picking up trash from the yard. It has a duration of fifteen minutes. Assuming that it starts at time = zero, it can finish as early as fifteen minutes later. We therefore can enter fifteen in the cell labeled EF. Putting gas in the mower and the weed whacker takes only five minutes. The logic of the diagram says that both of these tasks must be completed before we can begin trimming weeds, cutting the front grass, and edging the sidewalk. The cleanup task takes fifteen minutes, whereas the gas activity takes only five minutes. How soon can the following activities start? Not until the cleanup has been finished, since it is the longest of the preceding activities. Figure 6-2 Forward pass computations for yard schedule. In fact, then, the Early Finish for cleanup becomes the Early Start for the next three tasks. It will always be true that the latest Early Finish for the earlier tasks becomes the Early Start for subsequent tasks. That is, the longest path determines how early subsequent tasks can start. The Earliest Start for a task is the latest Late Finish of preceding tasks. That is, the longest path determines the earliest that a subsequent task can be started. www.erpvn.net Following this rule, we can fill in Earliest Start times for each task, as shown in Figure 6-2. This diagram shows that the project will take a total of 165 minutes to complete, if all work is conducted exactly as shown. We have just performed what are called forward pass computations to determine Earliest Finish times for all activities. Computer programs do exactly the same thing and also convert the times to calendar dates, making quick work of the computations. Rule: When two or more activities precede another activity, the earliest time that the final activity can be started is the larger of the durations of the activities preceding it. The time determined for the end or final event is the earliest finish for the project in working time. Once weekends, holidays, and other breaks in the schedule are accounted for, the end date may be considerably later than the earliest finish in working time. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement...
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This document was uploaded on 09/27/2013.

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