Skip to main content

Dummy activity and its application

Short answer

A dummy activity is an imaginary zero-duration, zero-resource activity shown by a dashed arrow in an arrow network, used only to show logical dependence. It applies when activities share predecessors, gives unique event numbers to parallel activities, and helps the network have one start and one end.

Define dummy activity and explain its application in scheduling.

A dummy activity is an imaginary activity of zero duration and zero resource, shown by a dashed arrow in an arrow (AOA) network. It only shows a logical dependence.

Applications in scheduling:

  1. Showing correct logic. When D depends on A and B but C depends on A only, a dummy from the end of A to the start of D keeps the logic right.
  2. Unique numbering. When two activities start and end at the same events (parallel activities), a dummy gives them different end events so that each has a unique i-j number.
  3. Connecting events so that the network has one start and one end event.
Rule: C depends on A only; D depends on A and B

(1) --A--> (2)
(1) --B--> (3)
(2) --C--> (4)
(2) - - dummy - -> (3)
(3) --D--> (5)

Dummy (2)->(3): D starts only after A and B end,
while C starts after A alone.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Project Engineering chapter 3 questions →