Lessons · Project management · activities and dependencies
Dependencies: which activity has to wait for which
A dependency says one activity cannot start or finish until another has: finish-to-start is the common one, and start-to-start, finish-to-finish and start-to-finish cover the rest.
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 painters arrive on Monday because the schedule said Monday, and the plasterers are still there. Somebody drew painting as starting on a date instead of after plastering finishes. The dependency is the fact; the date is only what the fact implied on the day the plan was drawn.
How to think about it
For every activity ask what must be true before it can start. Write the relationship, not the date: paint starts after plaster finishes is a finish-to-start link, and it stays true when plaster slips.
Worked example
Plaster → Paint, finish-to-start (FS)Paint starts when plaster finishes. Nine links in ten are this one.
Pour concrete → Cure, start-to-start (SS)Curing begins the moment pouring begins.
Write manual → Translate manual, finish-to-finish (FF)Translation cannot finish until writing has finished; they may run side by side.
Old system running → New system live, start-to-finish (SF)The old one may not finish until the new one has started. Rare, and usually a hand-over.
Plaster → Paint, FS with a 2-day lagPaint starts two days after plaster finishes, for drying. The lag is part of the link.
Your turn
Write the link for testing can start only when coding is complete.
Coding → Testing, -to-start
Solve one, graded on the server
The trap
Putting a date where a dependency belongs. A date does not move when its predecessor moves; a link does. Every fixed date in a schedule is a place the schedule can silently become wrong.