In this article, we will continue the topic of PERT and CPM and discuss about network constructiion. 

Rules of network construction:

There are number of rules in connection with handling of events and activities of project network that should be followed :

[i] Try to avoid arrows that cross each other

[ii]Use straight arrows.

[iii]No event can occur until an activity preceding it has been completed

[iv] An event cannot occur twice i.e. there must be no loops

[v]An activity succeeding an event cannot be started until that event has occurred .

[vi]Use arrows from left to right .Avoid mixing two directions, vertical and standing arrows may be used if necessary .

[vii]Dummies should be introduced only if it is extremely necessary.

[viii]The network has only one entry point called the start event and one point of emergence called the end or terminal point.


[i]Event numbers should be unique

[ii]Event numbering should be carried out on a sequential basis from left to right

[iii] The initial event which has all outgoing arrows with no incoming arrows is numbered as 1

[iv]  Delete all arrows emerging from all numbered events .This will create at least one new start event out of preceding events

[v]Number all new start events 2,3 and so on Repeat this process until the terminal event without any successor activity is reached .Number the terminal node suitably.

*The head of an arrow should always bear a number higher than one assigned  to the tail of the arrow.


Example Construct a network for each of the projects whose activities and their precedence relationships are  given below:

Soln: A,B,C are concurrent activities as they start simultaneously .B becomes predecessor of activities E and F.


In the next article, we will talk about Time Analysis for a project, which forms an important part of scheduling calcuations questions in GATE Mechancal Engineering. 


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Thanks. Please share some questions also.