Project Management - Rules of Network Construction

Project Management

Rules of Network Construction 

Part A - Discussion about 1. What is Network Analysis, 2. Difference between CPM (Critical Path Method) and PERT (Programme Evaluation and Review Technique), and 3. Rules of Network Construction.

Part B - YouTube Link for the Video on above discussion including solution of one illustration.

Part A

Network Analysis – Definition

What is Network Analysis?

Network analysis is a management technique that is adopted in planning and controlling of complex projects. It is a system of planning a project by analysing different activities associated with it. In network analysis, complex projects are broken down into smaller activities or tasks, which are then organised according to a sequence which must be logical keeping under consideration the total time and cost involved in completing the project as per the expectations of the owners, management and other stakeholders.

 

In the project management, a network diagram is prepared whereby all the project activities are represented visually. The diagram depicts the cost of various activities and the durations to complete the activities. The diagram also establishes a relationship between various tasks or activities of the project.

 

Network analysis ensures that the project is successfully completed economically and much before the expected time while exploiting minimum resources. Hence, network analysis reduces operational cost, total time, wastage of resources and conflicts in project management and execution.

 

Application of Network Analysis:

Network analysis is usually applied in the following types of projects:

a)       Construction of residential complex,

b)       Construction of commercial complex,

c)       Petro-chemical complex,

d)       Ship building,

e)       Aircraft manufacturing,

f)           Satellite mission development,

g)       Installation of pipe line, etc.

Network Analysis

Rules of Network Construction

 

A project can be viewed as a set of activities or jobs (also called tasks or operations) that are performed in a certain sequence determined logically or technologically. Therefore, the initial step in CPM/PERT project scheduling process is the determination of all specific activities that comprise the project and their interdependence relationships.

 

Once the activities comprising a project, as also the interdependency relationships among them, are clearly identified, they can be portrayed graphically by a network or an arrow diagram. Because the project planning function begins with a list of all the activities and their precedence relationships, the network can be constructed through the use of a series of arrows and nodes, thus conveniently expressing the sequential nature of the project.

 

Each of the activities that make up a project consumes time and resources and has a definable beginning and ending. The arrows, also called arcs, in a network represent the various activities of the project. Along with each arrow is given the description and the time estimate of the particular activity it is representing.

The circles at the beginning and at the end of the arrow represent the nodes, or the events, of beginning and completion, respectively, of the activity in question.

 

Rules of Network Construction

1.      One Activity – One Arrow

Each defined activity is represented by one and only one arrow in the network. Therefore, no single activity can be represented more than once in the network.

 

2.      All preceding activities must be completed

Before an activity can be undertaken, all earlier activities preceding it must be completed. Thus, a network should be developed on the basis of logical or technical dependencies between various activities of the project.

 

3.      Length and shape of the arrows are of no significance

The arrows depicting various activities are indicative of the logical precedence only. The length and shape of the arrows are of no significance.

 

4.      Arrow head marks completion and arrow tail marks start

The arrow direction indicates the general progression in time. The arrow head represents the point in time at which the ‘activity completion’ event takes place, while the arrow tail represents the point in time at which the ‘activity start’ event occurs. The events marking the start of activities are called tail-events while those marking the completion of activities are known as head-events.

 

5.      Merge Event and Burst Event

When a number of activities terminate at one event, that event is known as a merge event and it indicates that no activity emanating from the merge event may start unless all the activities terminating at the same merge event have been completed.

 

 

For example, in the above Figure (a), activities B, C, and D must be completed before undertaking the activity E. It may be noted, however, that it only implies that they should be completed before activity E begins, and not that they must be completed simultaneously.

 

On the other hand, an event which portrays the initiation of more than one activity is called the burst event. For example, in the above Figure (b), activity A should be completed before activities B, C, and D can be started.

 

6.      Events are identified by numbers

Events are identified by numbers. Each event should be identified by a number higher than that allotted to the event immediately preceding. In assigning numbers to the events, care should be taken that there is no duplication of event numbers in a network.

 

7.      Activities are identified by “i – j”

The activities are identified by the numbers of their starting and ending events. They are expressed as “i – j”, where “i” represents the starting event (or initial node) number, and “j” represents the ending event (or terminal node) number. Thus, the activities B, C, D, and E in Fig (a) above can be expressed as 3-6, 4-6, 5-6, and 6-7, respectively.

 

Event 3 represents the beginning of the activity B while event 6 represents the ‘completion of activities B, C, D, and the beginning of the activity E’.

 

8.      A network should have only one initial and one terminal node

 

9.      Parallel activities between two events are prohibited

Parallel activities between two events, without intervening events, are prohibited. Thus two or more activities cannot be identified by the same beginning and ending events. By implications, any two events should not be directly connected with more than one arrow. When two or more parallel activities in a project have the same head and tail events, dummy activities are needed in constructing the network. The dummy activities do not consume time or resources. Dummy activities are usually shown by arrows with dashed lines.

 

There are two types of dummies:

i.             Identity dummy, and

ii.           Logic dummy.

 

Identity dummies are used when two or more activities have same initial and terminal events.

 

Logic dummies are used when two chains of activities have a common event, although they are in themselves wholly or partly independent of each other. Thus, when two or more activities have some, but not all, of their inputs in common, the use of logic dummy resolves the problem of representation.

 

Thus, dummy activities, that are drawn only to adequately and correctly represent the given precedence relationships, are needed when

(i) Two or more activities in a project have identical immediate predecessor and successor activities, or

(ii)  Two or more activities have some (and not all) of their immediate predecessor activities in common.

 

It may be mentioned here that although the use of dummies provides initially a convenient means of depicting the dependency relationships between the activities, only a minimum number of dummies as may be needed to draw the network should be used.

 

An efficient network contains a minimum number of dummy activities required to portray the correct precedence relationships between the activities of a given project. Thus, while constructing an arrow diagram, the dummy activities may be included liberally and then on completion of the diagram the redundant ones eliminated.

Important Rule for Dummy Activity:

A Dummy Activity will start from the arrow-head of the immediate common predecessor and will finish at the arrow-head of immediate uncommon predecessor (if there is no immediate common successor) or at the arrow-tail of immediate common successor (if there is immediate common successor).

10.  Looping is not permitted in a network

Looping is not permitted in a network. In developing a network, it must be ensured that loops are not present. In case of a loop, precedence relationships, or dependencies, should be redefined to be related correctly.

Part B

YouTube Link for the video on above discussion including solution of one illustration.

Please click on the following YouTube Link:

Project Management - Rules of Network Construction