Project Schedules with Pert/Cpm

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Chapter 3 of Systems Analysis and Design in a Changing World explains the techniques and steps required to build a project schedule using the Gantt chart view in MS Project. This appendix provides a similar explanation of how to build a project schedule, but it is based on using a PERT/CPM chart or diagram for the schedule format. A Gantt chart and a PERT/CPM chart both provide essentially the same information about project activities and tasks. Each chart has unique strengths and weaknesses. As you learned in Chapter 3, a Gantt chart is a type of bar chart that is superimposed on a calendar. The primary strength of a Gantt chart is that the bars show the duration and project progress as compared to the days and weeks of the calendar. The calendar comparison provides an effective visual representation of the project timeline and helps you track project progress, because the Gantt chart shows what should have been accomplished by a specific date and what has actually been completed on that date. Chapter 3 illustrates an example of the tracking view of a Gantt chart. A PERT/CPM chart, as you will learn in this appendix, is a network type of diagram with boxes that represent the tasks or activities of the project, and with connecting arrows that represent the sequence and dependencies between tasks. The strength of a PERT/CPM chart is that, as a network, it provides a visual representation of the relationships between tasks of a project. During the development of the project schedule, and especially while trying to determine task dependencies, a PERT/CPM chart is an effective tool. PERT, which stands for Project Evaluation and Review Technique, was first developed in the 1950s and was used by the United States Department of Defense to organize, monitor, and control very large, complex defense projects. CPM, which stands for Critical Path Method, was developed independently, also in the 1950s. As its name implies, its primary objective was to determine not only the dependencies between tasks, but which tasks were on the critical path. These two methods have much in common, and in recent years most scheduling tools have taken the best attributes of each one and combined them into a single technique—thus the name PERT/CPM. In this appendix, we will first develop a PERT/CPM chart by hand so that you can learn and understand the basic concepts. Then we will illustrate a PERT/CPM chart in MS Project.


Developing a PERT/CPM chart is a five-step process: 1. 2. 3. 4. 5. Identify all the tasks for the project (that is, build a work breakdown structure or WBS). Determine the amount of work necessary to complete each task. For each task, identify the immediate predecessor tasks. Enter the tasks on a PERT/CPM chart, with connecting arrows for task dependencies. Calculate start and end times based on durations and resources.

As discussed in Chapter 3, the first three steps are always manual tasks and are often done in a brainstorming session. The last two steps happen automatically when entering the information into a scheduling tool such as MS Project. In Chapter 3, we provided guidelines in identifying and delimiting tasks. The chapter explained how to enter data for Steps 2 and 3, but detailed explanations were not included. We provide some additional guidance for those steps in this appendix.

Let’s start with the same set of tasks we identified in Chapter 3. Figure B-1 is a copy of that information in a document format. The first step—identifying all the tasks—can be done using any of the approaches explained in Chapter 3. Note that this example uses a hierarchical structure and numbers the tasks to show this hierarchy. By grouping individual tasks together into a larger activity, project managers can define summary activities and larger milestones that help to monitor the progress of the...
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