19.1 Activity Chart
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An activity chart is a network with directions and weights that represent flow of activity in a given project. The weights indicate the amount of time it takes while the vertices indicate the activity.
The details of activities are listed in what is called ‘Activity Table’. The following example explains everything you need to know for this section:
The following is an activity table for a given project:
Show this in an activity chart.
There are three ways of drawing an activity chart. The syllabus requires you to be familiar with all of the three and you are encouraged to use whichever style you are comfortable with.
Method 1: ‘Activity-on-node’ method
I personally think this is the easiest of all the methods to work with. In this method, activity name and weight are attached to vertices and a network diagram is formed by connecting different activities.
Starting with our example, activity A does not have a prerequisite which makes it the starting activity, so we will start off by connecting it with the start point, and since it is an activity-on-node method, A is written inside the vertex and weight (time) to complete A is written above it.
Next, from A goes two nodes B and C with time 2 and 1 respectively which are added to the activity chart below:
Next, D has a connection with B with a weight of 3:
Next one is interesting; E has a connection with C and D so we need to connect both C and D with this new node E:
Finally, node F is added and connected with the finish vertex as no further activity depends on it:
Method 2: ‘Activity-on-arrow’ method
Probably the most complicated of the three methods especially when it comes to using dummy activities (explained below).
Unlike previous method, this method attaches weight and activity name to the edge and not the vertex.
Continuing with our example, following is the activity chart until activity D which looks similar to the previous method, except now the activity names and weights have been moved to the edges:
From this point, think about it; if you connect two arrows, one from the node next to D and one from the node next to C, on which arrow are you going to place E(2)? This is a dilemma and you need a dummy activity to solve this.
A dummy activity has no name or no weight, and it is drawn as a broken edge. Its purpose is only to help in situations like above where one activity has prerequisites from multiple activities.
Whenever you draw an activity chart using this method, always do this questioning exercise that we did above to ensure connections are making sense.
Note that in the above, you can connect a dummy node in the following way too, and it is also correct as it conveys the same message:
Finally, activity F is added and the activity chart is completed:
Method 3: Activity on vertex and weight on edge
This method is a combination of the methods above where weights are put on the edge and activity name is put on the vertex.
Continuing with our example, the following is the activity chart until activity D which looks similar to the previous methods, except now the activity names are on the vertex and weights on the edges:
You are again faced with the same dilemma as in previous method; if you connect both C and D with E, on which edge will you put the weight? We are again going to solve this with a dummy activity.
A dummy activity in this case will be a new node X to which both nodes C and D are connected with weights 0 which is then connected to node E:
Finally, E is connected with F and the activity chart is finished:
You might find the following videos helpful related to this section:
For the other sections:
The following is the type of questions you can expect in exam:
Study notes of this section and other resources can be accessed here: