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Q.1 Describe the various ways of representing network diagram logic. .

Network Logic Diagrams
The logic development in project planning is an iterative process. Initial logic development starts after identification of the activities of the project and before scheduling process occurs. The logic development process is further refined during schedule development and optimisation. There are two common methods of logic diagramming which are referred as network logic diagrams. Before knowing the types of network logic diagrams, we should be familiar with rules to be followed while developing and analysing it.

The rules are described in the table

The two types of network logic diagram are:

Precedence Diagramming Method :
This method is also known as Activities On Node (AON). In this network logic diagram, each activity is represented by a node and connecting lines represents the relationships between activities. Each preceding activity controls the start and finish of the succeeding activity.
In precedence diagramming method, all the four dependency relationships can be implemented between the activities. Finish to Start dependency relationship is the most commonly used in this network logic diagram. Start to Finish dependency relationship is rarely used and it is typically used only by professional scheduling engineers. Usage of start-to-start, finish-to-finish, or start-to-finish relationship with project management software can produce unexpected results, since these relationships are not consistently implemented.
The figure shows the implementation of activities on node network logic diagram where the alphabets within the circle represents the activities of the project and linking lines shows the relationship between them.

Precedence Diagramming Method network logic diagram has the various advantages, they are:
  • It is amendable with most of project management software.
  • It is does not need introduction of a dummy activity in the network.
  • It offers greater flexibility as it can incorporate any of the four dependency relationships.

Arrow Diagramming Method
This method of network logic diagram is also known as Activity On Arrow (AOA). This is the historical basis for network diagrams. It was used for the development of PERT networks in the 1950s by the Department of Navy for tracking very large, complex Polaris program. In this method, each activity of the project is represented by an arrow between the nodes of the network and the nodes are mere symbols representing the connection points.
In AOA method of network logic diagram, finish to start relationships are used. The activities follow the order of precedence as defined by their immediate predecessors. When there is more than one immediate predecessor for an activity, the network must show that the activity can be started only after all of its immediate predecessors activities have been completed. The dummy activity defined above is used for this depiction in the network.
In AOA network logic diagram, the important points mentioned below should be followed to ensure the correct representation:
  • Activities of the project are represented by Arrows.
  • Events are numbered and are represented by Nodes.
  • Two dummy activities should be introduced to show the precedence relationships.
·         The figure 10.5 shows the representation of AOA, where alphabets on the arrow are the activities of the project and nodes between them represents the relationships between the activities.


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