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FIGURE 12-2. PERT sources (burst points) and sinks.

pleted (or begun). In Figure 12-2A, event 26 must take place prior to events 7, 18, and 31. In Figure 12-2B, the opposite holds true, and events 7, 18, and 31 must take place prior to event 26. Figure 12-2B is similar to "and gates" used in logic diagrams.3

In this chapter's introduction we have summarized the advantages and disadvantages of Gantt and milestone charts. These charts, however, can be used to develop the PERT network, as shown in Figure 12-3. The bar chart in Figure 12-3A can be converted to the milestone chart in Figure 12-3B. By then defining the relationship between the events on different bars in the milestone chart, we can construct the PERT chart in Figure 12-3C.

PERT is basically a management planning and control tool. It can be considered as a road map for a particular program or project in which all of the major elements (events) have been completely identified, together with their corresponding interrelations.4 PERT charts are often constructed from back to front because, for many projects, the end date is fixed and the contractor has front-end flexibility.

One of the purposes of constructing the PERT chart is to determine how much time is needed to complete the project. PERT, therefore, uses time as a common denominator to analyze those elements that directly influence the success of the project, namely, time, cost, and performance. The construction of the network requires two inputs. First, do events represent the start or the completion of an activity? Event completions are generally preferred. The next step is to define the sequence of events, as shown in Table 12-1,

3. PERT diagrams can, in fact, be considered as logic diagrams. Many of the symbols used in PERT have been adapted from logic flow nomenclature.

4. These events in the PERT charts should be broken down to at least the same reporting levels as defined in the work breakdown structure.

(A) GANTT CHART

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