Although both formats are only alternative ways to represent a project network,
there might be reasons to have a preference towards one of the formats. Probably,
many project managers will rely on the activity-on-the-node format, since this
allows for the incorporation of generalized precedence relations (see Sect. 2.2.3),
and is embedded in most resource allocation models of commercial software tools.
However, some people might feel a preference for the activity-on-the-arc format,
since the first scheduling principles (e.g. PERT (discussed at the end of this chapter)
and CPM (Chap. 3)) have originally been developed for AoA networks. In the
remainder of this book, we rely on the AoN format to represent project networks.
More precisely, it is always assumed that a project is represented by an activityon-
the-node network where the set of nodes, N, represents activities and the set
of arcs, A, represents the precedence constraints. The activities are numbered from
1 to n (i.e. jNjDn), where node 1 and node n are used to denote the dummy start
and dummy end activity, respectively. The dummy start activity is a predecessor
for all activities in the network and is used to denote the start of the project. In a
similar way, the dummy end activity n denotes the finish of the project and is a
successor for all activities of the project. No further dummies are used in the AoN
format.