Logic Ties

In a given network, it is common to encounter logic ties with no durations. These are called "dummy" activities and are added to the network to portray all predecessor relationships in a graphical form. As well as being called dummies, these can be referred to as restraints.

Normally, Activity G would begin with Activity E's completion, however, the activities have been defined to restrain Activity G's start until both B and E are completed, as illustrated in Figure 3-7.

Figure 3-7. "Dummy" Restraint Network

Figure 3-7. "Dummy" Restraint Network

Problem 3-2: Network Workshop

The following example illustrates the relationship between Activity Definition, Durations and Dummy Restraints. Given the network as shown in Figure 3-8 with the durations in days already established, determine the Critical Path.


The Critical Path as defined earlier is the longest duration chain in a logic network and it determines the total project/network duration.

Figure 3-9 illustrates the Critical Path solution. The heavy lined activities on the Critical Path are called Critical Activities. Now that the Critical Path has been determined, analysis of the network can begin.

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