An Alternative Representation of Project Activity Networks: Activity on Arcs and Nodes (AoAaN)

Activity-on-arc (AoA) and activity-on-node (AoN) project network representations have been used in construction scheduling for many decades. But due to the primary information that they emphasize—the activities themselves in the AoA graphs, and the precedence relationship structure in the AoN graphs—they also have significant limitations. In this paper, we develop a hybrid representation approach named Activity-on-Arcs-and-Nodes (AoAaN). This novel network representation transforms all project activities into arcs (as in the AoA representation) but retains all precedence relationships between activities (as in AoN). To develop this alternative network representation, first, we establish its theoretical drawing principles, which mostly involve how to deal with different precedence relationship types (FS, SS, SF, FF) in basic networks. Then, we proceed with the calculation and analysis of more realistic project examples with a larger number of activities. Advantages of the new AoAaN is that it allows a simpler and more fine-grained determination of the critical path, while facilitating computer calculation via a Dependency Structure Matrix (DSM) that purely contains numerical information. Additionally, the proposed AoAaN allows handling coupled (interdependent) activities, a type of relationship that had previously hampered analysis of networks. Due to its flexible modeling capabilities and calculation simplicity, we suggest the AoAaN representation be added to project management courses as well as be used by project schedulers as a more capable alternative to the traditional AoA and AoN representations.