ABSTRACT
The first step in CPA is to prepare a list of all the activities that make up the project and, for each, identify the duration and dependent activities; that is, activities which have to be completed before another can start. Let’s use the house building example:
ACTIVITY DESCRIPTION DURATION WEEKS DEPENDENT ACTIVITIES
A Access road 3 B Footings 2 C Foundations 2 A, B D External walls 6 C E Internal walls (lower) 4 C F floors 2 E G Internal walls (upper) 3 F H Roof trusses 2 D J Roof tiles 2 H K Gutters/drain pipes 1 J L Soakaway 1
We can now draw a network of arrows and nodes – the so-called ‘Activity on Arrow’ diagram, in which the arrows represent the activities (each identif ied and with the duration marked on it) and the nodes (sometimes called ‘events’) are the start or completion of an activity. This shows how the activities depend on one another. The dotted line connecting node 3 to node 2 is a ‘dummy activity’. This shows dependence and means that activity C cannot start until activities A and B have both been completed. Dummy activities have no duration.
