Rules for Drawing Network Diagram

March 05, 2022 Post a Comment

Network Diagram Representation

In a network representation of a project few definitions are used

1. Action

Any individual operation which makes use of resources and has an finish and a starting is chosen every bit activity. An arrow is generally used to narrate an action with its head representing the direction of progress in the project. These are divided into four classes

Predecessor activity - Activities that ought to be completed immediately previous to the start of another activity are known every bit predecessor activities.
Successor activeness - These are those activities that cannot be started until one or more of other activities are finished merely immediately succeed them.
Concurrent activeness - These are activities which can be accomplished concurrently. It may exist noted that an activity can be a successor or a predecessor for an event or it may be concurrent with 1 or more activities.
Dummy activity - An activity which does not use any type of resources merely simply depicts the technological dependence is known as dummy activity.

The dummy activity is included in the network to clear the activity pattern in the next two situations

To fix activities with common starting and ending points noticeable
To observe and maintain the right precedence relationship between activities that is not linked by events.

For instance, take a situation where A and B are concurrent activities. C is reliant on A and D is reliant on A and B both. This type of situation can exist handled with the use of dummy action every bit shown in the effigy.

ii. Issue

An event signifies a point in time representing the completion of several activities and the starting of new ones. This is typically symbolizes by a circle in a network which is as well known as node or connector.

The events are divided into three categories

Merge event - Event in which more than one activity comes and connects an event is called as merge event.
Burst upshot - It is upshot in which more than ane activity leaves an event.
Merge and Burst event - An activeness tin be merge and burst result simultaneously, as regard some activities it tin exist a merge effect and with some other activities information technology may exist a flare-up outcome.

3. Sequencing

The kickoff requirement in the development of network is to keep the precedence relationships. In order to prepare a network, the subsequent points must exist taken into considerations

What job or jobs follow it?
What job or jobs could run concurrently?
What task or jobs precede information technology?
What controls the outset and stop of a job?

As all further calculations are on the basis of network, it is essential that a network exist drawn with total care.

Rules for Drawing Network Diagram

Rule 1

Each of the activity is symbolized by one and merely one arrow in the network

Rule 2

No 2 activities can be recognized by the same cease events

Rule 3

To clinch the correct precedence relationship in the pointer diagram, various questions must exist tested every time any activity is added to the network

What activeness must exist finished immediately before this activity can start?
What activities must occur at the same time with this activity?
What activities must follow this activity?

In example of large network, it is necessary that certain proficient habits exist applied to draw an like shooting fish in a barrel to follow network

Strive to avoid arrows which cross each other
Brand use of straight arrows
Practise not effort to represent duration of activity through its arrow length
Employ arrows from left to right. Avert mixing two directions, vertical and continuing arrows can be utilized if essential.
Practice dummies freely in rough typhoon only terminal network should be free of whatever redundant dummies.
The network should have only one entry point known every bit start upshot and ane indicate of emergence which is known as the end issue.

Common Errors in Drawing Networks

The three types of errors are most oft seen in drawing network diagrams

1. Dangling

To cut off an activity prior to the completion of all activities in a network diagram is referred to every bit dangling. As reveal in the figure activities (5 - 10) and (6 - vii) are not the final activities in the network. And so the diagram is incorrect and shows the error of dangling

ii. Looping or Cycling

Looping error is also called as cycling error in a network diagram. Making an endless loop in a network is called equally error of looping as revealed in the following figure.

iii. Redundancy

Needlessly put the dummy action in network logic is called as the error of redundancy as reveal in the diagram beneath

Advantages and Disadvantages

PERT/CPM has the subsequent advantages

A PERT/CPM chart clearly defines and makes visible dependencies between the elements,

PERT/CPM makes easy identification of the disquisitional path and makes this noticeable,

PERT/CPM makes easy identification of late start, early first, and slack for each action,

PERT/CPM gives for potentially reduced project period considering of better understanding of dependencies leading to enhanced overlapping of activities and tasks where feasible.

PERT/CPM has the subsequent disadvantages:

There tin can be possibly hundreds or thousands of activities and individual dependency relationships,

The network charts like to be big and unwieldy requiring numerous pages to impress and need special size paper,

The lack of a timeframe on the majority PERT/CPM charts makes it hard to demonstrate status though colours can help (e.g., specific colour for completed nodes),