Activity-on-arrow (AOA) network
The classic textbook PERT notation — numbered event circles, activities as labelled arrows, and dotted dummy activities auto-inserted at multi-predecessor merges. Written in the same activity-on-node DSL; Schematex builds and numbers the event graph.
For the PMP student
Before activity-on-node won, project networks were drawn activity-on-arrow (AOA / ADM): the arrows are the work and the nodes are events — the instants when activities start and finish. It's the form on Investopedia and in older textbooks, and it's what layout: aoa produces.
You still write activity-on-node. The DSL is identical to every other PERT example — tasks, durations, after: dependencies. Schematex converts it: each activity gets a head event, and the events are numbered so every arrow runs from a lower id to a higher one (the classic i-j rule).
Dummy activities. AOA can't show two activities merging into one without help, so wherever an activity has multiple predecessors a dummy (dotted, zero-duration arrow) is inserted. Here test code depends on both programming and conversion, and user test on both test system and training — each merge gets dummies that carry the dependency without representing real work.
The critical path is still computed. The forward/backward pass runs on the event graph and the critical activities are drawn as bold red arrows: create schedule → programming → test code → test system → user test (70 days).
One caveat. AOA can only express finish-to-start logic — there's no way to draw a start-to-start or finish-to-finish relationship as an arrow-between-events. If your network uses SS/FF/SF or lag, those are flattened to FS with a warning. For real scheduling, prefer the default network (AON) layout; reach for aoa when you need to match a textbook figure.