Programme Evaluation and Review Technique (PERT) and Critical Path Method (CPM) (part-3)

List out all the activities involved in a project. Say, for example, in building construction, the activities are:

(i) Site selection,

(ii) Arrangement of Finance,

(iii) Preparation of building plan,

(iv) Approval of plan by municipal authorities,

(v) Purchase of materials,

(vi) Digging of foundation,

(vii) Filling up of foundation,

(viii) Building superstructure,

(ix) Fixing up of doorframes and window frames,

(x) Roofing,

(xi) Plastering,

(xii) Flooring,

(xiii) Electricity and water fittings,

(xiv) Finishing

Þ     Once the activities are listed, they are arranged in sequential manner and in logical order. For example, foundation digging should come before foundation filling and so on.

Þ     After arranging the activities in a logical sequence, their time is estimated and written against each activity. For example: Foundation digging: 10 days, or 1½ weeks.

Þ     Some of the activities do not have any logical relationship, in such cases; we can start those

activities simultaneously. For example, foundation digging and purchase of materials do not

have any logical relationship. Hence both of them can be started simultaneously. Suppose

foundation digging takes 10 days and purchase of materials takes 7 days, both of them can

be finished in 10 days. And the successive activity, say foundation filling, which has logical

relationship with both of the above, can be started after 10 days. Otherwise, foundation

digging and purchase of materials are done one after the other; filling of foundation should

be started after 17 days

Þ     Activities are added to the network, depending upon the logical relationship to complete the

project network.

Some of the points to be remembered while drawing the network are:

1. There must be only one beginning and one end for the network.

2.  Event number should be written inside the circle or node (or triangle/square/rectangle etc). Activity name should be capital alphabetical letters and would be written above the arrow. The time required for the activity should be written below the arrow.

3.While writing network, see that activities should not cross each other. And arcs or loops should not join Activities.

4. While writing network, looping should be avoided. This is to say that the network arrows should move in one direction, i.e. starting from the beginning should move towards the end.

5.When two activities start at the same event and end at the same event, they should be shown by means of a dummy activity .Dummy activity is an activity, which simply shows the logical relationship and does not consume any resource. It should be represented by a dotted line . 

6.When the event is written at the tail end of an arrow, it is known as tail event. If event is written on the head side of the arrow it is known as head event. A tail event may have any number of arrows (activities) emerging from it. This is to say that an event may be a tail event to any number of activities. Similarly, a head event may be a head event for any number of activities. This is to say that many activities may conclude at one event.