Network Analysis — Diagram, Terms and Construction Rules

Foundational Terms

• Activity: a specific task or job that consumes time and/or resources, represented by an arrow in the network diagram, with the arrow's tail and head marking its start and finish.
• Event (Node): a specific point in time marking the completion of one or more activities and the start of others — represented by a numbered circle, and consuming no time or resource itself.
• Dummy Activity: an activity consuming zero time and zero resource, drawn with a dashed arrow, used purely to preserve the correct logical dependency between two activities when the real activities themselves don't share a natural common event.

Rules for Constructing a Network Diagram

• Every activity must have one, and only one, preceding (tail) event and one succeeding (head) event.
• No two activities may share both the same tail event and the same head event (a dummy activity is inserted to resolve this if it would otherwise happen).
• The network must have exactly one starting event (no incoming arrows) and exactly one ending event (no outgoing arrows).
• No closed loop (a path that returns to an event already passed) is permitted — a network always proceeds forward in time.
• Events are conventionally numbered so that every arrow points from a lower-numbered event to a higher-numbered event. …