# Problem-Solving Techniques #10: Project Network Diagrams

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Everybody. This is eugenia lachlan lecture and computing at the national college of ireland and and welcome to my series of short videos on problem. Solving techniques in video.
Number. Were going to take a look at project network diagrams. So first off what is a project network diagram well its a graphical representation of a project schedule that shows the logical relationships and sequencing of activities that make up a project.
This type of diagram is useful for planning tracking and controlling any project from start to finish for this reason is a very popular tool of course for project managers. But also people like business analysts and other types of analysts will also make use of project network diagrams. A project network diagram is a technique for showing activity sequencing it gives us a schematic display of the logical relationships among our sequencing of project activities.
So every project can be broken down into activities on our diagram. Here. We have six activities.
These activities are labeled from a to f. And they represent the arrows that are on the diagram here. So each arrow in this case.
Represents an activity and each node at the beginning of the arrow. Lets take a look at activity. A has node number one at the start of the arrow and load number two at the end of the arrow and represent this tells us the sequence of activity.
So a is followed by b. Which in turn is followed by c. Which in turn is followed by f.
We can read that from this diagram similarly. Theres another path through this diagram or a can be followed by activity d. Which is followed and turn by e and finally followed by f.
So. This project network diagram at a glance lets us see what the sequence of activities through this project are so when should you use a project network diagram well theyre very useful tools. When you are planning a new process or if youre involved in improving an existing process for new processes you will have to determine the logical sequence of activities for any solution that you propose and we do this because activities often cause changing problems on projects for example.
If you have two activities. Requiring the same resource. They cannot be completed at the same time so we want to use a project network diagram.
When we are planning scheduling or controlling a new program or product development effort. These type of diagrams can help us document and track a complex project. Its an existing a planned project and they can also help us designate.
Whats called critical path. Which ill come back to in a few moments and show other interrelationships between activities. We can also use these network diagrams to ensure time and resource management and they can help us reduce project costs through a coordination and communication.
So if we can do all this with something as simple as a project network diagram. We will indeed have quite a powerful tool and to help us with our project. Which hopefully will get us to a solution to solve our problems.
So how do you draw a project network diagram when method i have chosen here is the activity on arrow or aoa method there are other methods. But im going to just use this one here and the reason why im using this one is a very simple technique. We just need two symbols.
We need an arrow first of all which represents the activity and we need a circle. Which we call a node to represent an event so on the simple diagram at the very bottom of the screen. Here we have one activity.
Which is called activity a so thats put on the arrow and hence the name activity on arrow and venture. Number one represents the start of activity. A and thats in the node on the left hand side and event.
Number two on the right hand side. This represents the end of activity.

A so the numbers inner circles are event numbers. So lets take a look at a step by step procedure for creating our project network diagram. Well first step is that we find all of the activities that start at node number one so in our simple example here.
Weve got just one activity. Thats activity. A and that starts at node number.
One so we draw that coming out of node number. One step number two then we draw their finished nodes and draw arrows between node number one and those finished nodes. So you can see here.
We have one arrow going from node number one to the next node. Which is node number two and then we put the activity. Letter and a in this case and duration at one lets say thats one day in this case.
Im on the diagram and two for whatever. The activity is we put the activity name and its duration on the arrow. Sometimes youll see this as ive shown here with the activity on top and the duration in the bottom.
But often youll also see written as activity. A equals one or something similar and the good idea here is to make sure that it is simple and that you dont get too cluttered. With too.
Many words and names particularly if an activity has a long name you might be better off using a letter or a code to represent that activity so continue drawing the network diagram usually working from left to right. And theres two very important things that you should watch out for when youre drawing a project network diagram. You should look for bursts and merges a burst occurs when a single node is followed by two or more activities.
So you can see on our diagram. Here that node number two is followed by two activities their activities be and activities d. So they this represents a burst and the second thing.
You should look out for is a merge. Which is the opposite of a burst and immersed and emerges. When two or more nodes precede a single node.
So you can see in our diagram. Here. That node number five is preceded by activities c.
And e. And these are very very important for people to watch out for and to understand because this is the source of most errors and in my classes project management classes. These are the areas for students make the most mistakes and also in business project managers have to really really watch out for the bursts and marriages in their project network diagram.
Because this too can lead to errors. When they are being drawn so this m project network diagram here is quite simple to read. Therefore.
There are two parts to this diagram activity. A followed by activity b. Followed by c.
And then followed by f. So thats one path activity. A followed by d and then e and then f thats a second path and we can see the sequence of activities here so for example.
We can see that activity c must follow activity b. In fact activity c cant start until b is complete an activity f cant start until both activities c and e are complete one of them is complete it still cant start. According to this diagram.
So lets now take a look at an example and this table here is typical of a table. I will give to students when asking them to draw a project network diagram. Its very simple weve got three columns here.
We list our activities. We got nine activities in this example here labeled from eight.

I then we have dependencies in the center. And this is where we show what which activity is dependent on other activities being complete and on the third and rightmost column. We have the duration.
So we just put in the numbers here in my example here. Im going to use the duration of days. So the noc duration of four represents and this activity will take four days to complete so lets quickly look at this table activity.
A is not dependent on activities. We just leave that blank or just put in a different. And if its a duration of four days activity b is not dependent on activity.
Any other activity and it has a duration of three days when we come to activity activity c. In this example. We can see that activity c is dependent on a being complete and it has a duration of two days.
We can also see that activity d is also dependent on a and complete. And it has a duration of five days or table. And data for the diagram is getting a little bit more complicated here activity e.
Is dependent on b. Being complete activity f. Is dependent on c.
Being complete g is dependent on d and h is dependent on being complete finally activity. I is dependent on activities f g. And h being complete so straight away.
I can see that my diagram here is going to have some bursts and merges on the two this is that in the dependency column you can see for example activity. A lists it twice and down at the bottom activities f g. And h.
All dependent on activity. Ive been complete so i know before i draw. My diagram that im going to require bursts and merges so on this picture here down in the bottom right hand corner.
I have a small version of the table that we have just seen. But the activities and dependencies and durations listed so for you can see those in the table and in my diagram. I have drawn a project network diagram to represent this particular table here so lets take a look at the first activity.
So im going to look at activities. A and b. Together.
Because and they can start at node number one because they are not dependent on any other activity being complete and i draw my finish nodes node number 2 and node number tree to represent the ends of activities. A and b. I continue on from left to right i can see that ive got a birth death.
After node1 a burst after note. 2. Ive got a merge at node number.
7. And this allows me to see that my last activity. I which follows f g.
And h. As hinted on the table is the last activity on my diagram. So it may put the virtual while to pause.
The video at this stage to try and understand the link between the table and the diagram on the left hand side here finally the critical path through this diagram. You can see that there are three possible paths. Here and the longest path highlighted in red takes.
14 days. The other two paths take 12 and nine days respectively and the critical path through this project is 14 days therefore the overall duration of the project is 14 days. If you found this to you a useful tool to have been your problem solving techniques you read about this with many more examples from my new book and introduction to business systems analysis published by the liffey press and available through amazon thank you for your attention in watching this video.
I hope you found it useful .

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