Fundamentals Of Project Management

Critical path the critical path is the longest path

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Unformatted text preview: now how to do them manually. My belief is that unless you know how the computations are done, you do not fully understand the meanings of float, early and late dates, and so on. Further, you can easily fall prey to the garbage-in, garbage-out malady. So here is a brief treatment of how the calculations are done by the computer. (For most schedules, the computer has the added bonus of converting times to calendar dates, which is no easy task to do manually.) First, consider what we want to know about the project. If it starts at some time = zero, we want to know how soon it can be finished. Naturally, in most actual work projects, we have been told when we must be finished; that is, the end date is dictated. Further, the start date for the job is often constrained for some reason: resources won’t be available, specs won’t be written, or another project won’t be finished until that time. So scheduling usually means trying to fit the work between two fixed points in time. Whatever the case, we want to know how long the project will take to complete; if it won’t fit into the required time frame, then we will have to do something to shorten the critical path. In the simplest form, computations are made for the network on the assumption that activity durations are exactly as specified. However, activity durations are a function of the level of resources applied to the work, and if that level is not actually available when it comes time to do the work, then the scheduled dates for the task cannot be met. It is for this reason that network computations must ultimately be made with resource limitations in mind. Another way to say this is that resource allocation is necessary to determine what kind of schedule is actually achievable. Failure to consider resources almost always leads to a schedule that cannot be met. Failure to consider resource allocation in scheduling almost always leads to a schedule that cannot be achieved. The first step in network computations is to determine where the critical path is in the schedule and what kind of latitude is available for noncritical work under ideal conditions. The ideal situation is one in which unlimited resources are available, so the first computations made for the network are done ignoring resource requirements. This is the method that will be described in this chapter; for information on resource allocation methods, the reader is referred to scheduling software manuals. NETWORK RULES Two rules are applied to all networks in order to compute network start and finish times. (Other rules are sometimes applied by the scheduling software itself. These are strictly a function of the software and are not applied to all networks.) Rule 1: Before a task can begin, all tasks preceding it must be completed. Rule 2: Arrows denote logical precedence. The length of the arrow or its angular direction have no significance. (It is not a vector but a scalar.) Initial schedule computations are made on the...
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This document was uploaded on 09/27/2013.

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