Network diagram

A project network diagram is a schematic display of the logical relationships (dependencies) among the project activities. It shows the sequence in which activities are to be done, and is used to find the critical path, float and the project duration. It is produced in the "Sequence activities" process (precedence diagramming).

Types

1. Activity-on-Node (AON) / Precedence Diagramming Method (PDM)
   • Boxes (nodes) represent activities; arrows show dependencies.
   • Supports four relations: finish-to-start (FS), start-to-start (SS), finish-to-finish (FF), start-to-finish (SF), with leads and lags. Most commonly used.
2. Activity-on-Arrow (AOA) / Arrow Diagramming Method (ADM)
   • Arrows represent activities; nodes represent events. Uses only finish-to-start and may need dummy activities.

The same logic (B and C follow A; D follows both B and C) in both forms:

AON:   [A 3d] --> [B 5d] --> [D 2d]
          \                   ^
           +-> [C 4d] -------+

AOA:  (1)--A-->(2)--B-->(3)--D-->(5)
                |        ^
                C        : dummy
                |        :
                +-->(4)..:

(In AOA, B and C cannot both join nodes 2 and 3, so a dummy from 4 to 3 shows that D also depends on C.)

Information in a node

Activity name, duration, earliest start (ES), earliest finish (EF), latest start (LS), latest finish (LF) and float.

Uses

• Show the order of work.
• Calculate the critical path via the forward pass (ES, EF) and backward pass (LS, LF).
• Float = LS − ES = LF − EF.
• Identify parallel activities, bottlenecks and schedule compression options.
• Basis for the Gantt chart and resource scheduling.

Steps to draw

1. List activities from the WBS.
2. Find the predecessors of each.
3. Draw a start node and arrange activities from left to right.
4. Link dependencies; avoid loops.
5. Add durations and calculate.

Advantages and limits

Clear logic and critical path identification; but large networks become complex.