Network Analysis

“Network analysis is a generic term for a family of related techniques developed to aid management to plan and control projects”.

PERT (Programme Evaluation and Review Technique) and CPM (Critical Path Method) are network based methods to assist in the planning, scheduling and control of projects.

A project is defined as “a collection of interrelated activities with each activity consuming time and resources”. The objective of PERT and CPM is to provide analytic means for scheduling the activities.

(i). Activity:

This is a task or job of work which takes time and resources eg. Build a wall, dig foundations, etc. An activity is represented in a network by an arrow The head indicates ending and tail indicates beginning of activity.

(ii). Event:

This is a point in time and indicates the start or finish of an activity. Eg. Wall built, foundations dug, etc. An event is represented by a node or circle. O

(iii). Dummy activities:

A correct precedence relationship may sometimes require the use of a dummy activity. The dummy activity provides the required logical sequencing relationship. However it does not alter scheduling because it is a zero time activity.As an example, activities r & s have the following precedence requirement.

Activity Precedencer ps p or q

The following network does not satisfy the precedence requirement.

p r

q s

1

The dummy activity is used to satisfy the precedence requirement.

Dummy activity is represented by a dashed arrow

Another used dummy activity is when two parallel activities have the same and end nodes.

(iv). Critical Path:

The critical path of a network gives the shortest time in which the whole project can be completed. There may be more than one critical path in a network and it is possible for the critical path to run through a dummy.

The network analysis will be more clear from the following example.

q s

n

o

m p

n

o

p

m

Dummy

2

p r

3