What is a Network Diagram?
Network diagrams are graphical representations of activity with their relationships. Network diagrams are used to schedule and schedule calculations to determine critical and critical paths.
Network Diagram Type
There are two types of network diagrams used in the development of a schedule.
Arrow Network or AOA (Activity on Arrow) or ADM (Arrow Diagramming Method)
Network Node or AoN (Activity or Node) or PDM (Precedence Diagramming Method)
1) Arrow Network or ADM (Arrow Diagramming Method)
ADM (Arrow diagramming method) is a type of network diagram where activity is represented by arrows, which are connected through nodes. The arrow tails are the start of the activity, and the arrowhead is the result of the activity. The length of the shaft is often proportional to the duration of the event. The arrow network only indicates the complete start or ‘FS’ relationship between activities.
An activity originates and ends at a node. Nodes are used to represent the beginning or end of the following activity. Starting a node of activity is also called an inode activity. And the end node of activity is also called a j-node of activity. This method is also known as the method of I-J diagram.
The relationship between activities often requires dummy activity to represent them correctly. Dummy activity has no duration. This is only introduced to build a complex relationship between activities that can not be set otherwise. A dummy activity is represented by dashed lines in network diagrams. In the example below, activity C will begin when activity B and activity E are completed. And activity F will start when activity E speaks Finnish. So it is necessary dummy activity to establish the relationship between C and E which can not be formed from the activity.
Method to create Arrow Network Diagram
Let’s see how to make the arrow network diagram. Consider the following data where there are 6 activities from A through F. The predecessor of each activity is written next to it.
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To draw an arrow diagram draw a vertex to represent the beginning of the project. In this case, node 1 represents the project started (see solutions below). Remember that you can count the nodes you want. You can enter nodes as 1, 2, 3 or 10, 20, 30, etc. Now see activity A has no predecessor. So, draw an arrow that comes from node 1 and ends at node 2. Since B and C both have their predecessor A then they must come from node 2 (end of activity A) and end up at their respective nodes (3 and 4 in this case ). Similarly, draw activity D, E. Because activity F has two predecessors so that the arrows must originate when D and E are finished, or from node 5. Node 6 represents the end of activity F and also the end of the project.
Lags and leads can also be shown on the ADM network, but new activities must be drawn to show lag or leads. In the example below, a hunk of concrete is placed that takes seven days of healing time until the shape can be disarmed. This relationship can be shown in ADM as below.
The ADM method has contributed greatly to network diagrams in the past. But this method is no longer used. Now a network diagram is created using the precedent diagram or PDM method. Scheduling software such as Primavera P6 also uses the PDM method for network diagrams.
2) Node Network or PDM (Precedence Diagramming Method)
PDM (Precedence diagramming method) is a type of network diagram where activity is represented by a node, which is interconnected through arrows. This arrow shows the relationship between activities. Methods of precedent diagrams, the four types of relationships can be shown between activities. This relationship is Finish to Start ‘FS,’ Start to Start ‘SS,’ Finish to Finish ‘FF’ and Start to Finish ‘SF.’
Method to create a Precedence Network Diagram
Let’s see how to make a preliminary network diagram. Consider the following data where there are 6 activities from A through F. The predecessor of each activity is written next to it.
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To create a preliminary diagram, first draw a box to represent activity A. You can also start by drawing the initial carton of Project and connecting it to activity A. Since B and C both have A’s predecessors then now draw two boxes for B and C and Connect them with Activity A. Similarly draw the boxes for D and E and relate them to the activities of B and C respectively. Now create a box for activity F and connect to activity D and E.
From the above discussion, we can list some of the different methods of ADM and PDM diagrams. As an example:
PDM diagram method is easy and widely used. The ADM method is not used now.
No need to include dummy activity to build complex relationships in PDM. You can establish relationships through the relationship path. At ADM, dummy activity is needed to build complex relationships.
The four types of relationships can be drawn in PDM. In ADM only Finish to Start (FS) relationship can be drawn.
In PDM, slowness and outlook can be shown on the line of relationships. But in ADM, separate activities need to be added to show lag and leads.
There are two basic types of network diagramming techniques. ADM or Arrow Network Diagram and PDM or Precedence Network Diagram. In ADM, activity is shown as a temporary arrow in PDM; activity is displayed as a node or box. PDM is easy to use and can accommodate the complexity of the schedule. PDM is used in different scheduling software such as Primavera P6.