Constructing a network

The first stage in constructing a network for a project is to consult with the technical experts and summarise the information that they provide in a table, as in the following simple example.

The predecessors impose constraints on the project: C cannot begin until A has been completed, whereas D cannot begin until both A and B have been completed.

There are two types of network that we can draw for this project:

1.  activity-on-arrow (AOA)

2.  activity-on-node (AON)

The dummy activity (shown by the dotted line) is needed in the AOA network to show the predecessors correctly, i.e. that D depends on both A and B, but C depends only on A.  AOA networks often need several dummy activities.  AON networks do not need dummy activities.

Which type of network is better?

Students often find AON networks a little easier to draw, and this can seem like a big advantage when doing it for the first time.  However, some of the more advanced types of network analysis are best done using an AOA network.

Every well educated student should be able to draw and analyse either, so that they are never thrown into confusion if they come across the one they haven’t learnt to use.  For people in employment, if your boss has a preference, then that’s the one to use.