Page 174 - DCAP304_DCAP515_SOFTWARE_PROJECT_MANAGEMENT

Software Project Management

Notes
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Caution When work is delegated like this, the need for constant feedback and co-ordination
becomes an important senior management preoccupation.

9.1.2 Drawing the CPM/PERT Network

Each activity (or sub-project) in a PERT/CPM Network (see figure 9.1) is represented by an
arrow symbol. Each activity is preceded and succeeded by an event, represented as a circle and
numbered.

Figure 9.1: CPM Network

PERT

At Event 3, we have to evaluate two predecessor activities - Activity 1-3 and Activity 2-3, both of
which are predecessor activities. Activity 1-3 gives us an Earliest Start of 3 weeks at Event 3.
However, Activity 2-3 also has to be completed before Event 3 can begin. Along this route, the
Earliest Start would be 4 + 0 = 4. The rule is to take the longer (bigger) of the two Earliest Starts.
So the Earliest Start at event 3 is 4.
Similarly, at Event 4, we find we have to evaluate two predecessor activities - Activity 2-4 and
Activity 3-4. Along Activity 2-4, the Earliest Start at Event 4 would be 10 wks, but along Activity
3-4, the Earliest Start at Event 4 would be 11 wks. Since 11 wks is larger than 10 wks, we select it
as the Earliest Start at Event 4. We have now found the longest path through the network. It will
take 11 weeks along activities 1-2, 2-3 and 3-4. This is the Critical Path.

Did u know? CPM was the discovery of M.R. Walker of E.I. Du Pont de Nemours & Co. and
J.E. Kelly of Remington Rand, circa 1957. The computation was designed for the UNIVAC-
I computer. The first test was made in 1958, when CPM was applied to the construction of a

168 LOVELY PROFESSIONAL UNIVERSITY