Lessons · Project management · the network diagram
The network diagram: the activities drawn as a chain of boxes and arrows
A network diagram draws each activity as a box and each dependency as an arrow, so every path from start to finish can be seen and added up.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
The sponsor asks how long the project takes. Adding all the durations gives 24 days; the answer is 12, because half the work runs in parallel. Only the diagram shows which activities are side by side and which are in a line.
How to think about it
Draw a box per activity with its duration inside. Draw an arrow from each predecessor to each successor. Then trace every route from the first box to the last and add the durations along it: each route is a path, and the longest path is how long the project takes.
Worked example
A 3 days, no predecessor. B 4 days after A. C 2 days after A. D 5 days after B and CThe list a schedule starts from.
A → B → D, and A → C → DTwo paths. B and C run side by side after A; D waits for both.
A-B-D = 3 + 4 + 5 = 12 days. A-C-D = 3 + 2 + 5 = 10 daysEach path added up along its arrows.
The project takes 12 daysThe longest path decides; the shorter path has 2 days of room.
Your turn
Write how long the project takes once every path is added up.
The project takes as long as the path.
Solve one, graded on the server
The trap
Adding every duration. Activities in parallel do not add. The diagram exists so that the eye sees which ones are side by side.