Dependency (project management)
In a project network, a dependency is a link among a project's terminal elements.[citation needed]
The
Standard types of dependencies
There are four standard types of dependencies:[2]
- Finish to start (FS)
- A FS B means "activity A must finish before activity B can begin" (or "B can't start until A has finished").[3]
- (Foundations dug) FS (Concrete poured)
- A FS B means "activity A must finish before activity B can begin" (or "B can't start until A has finished").[3]
- Finish to finish (FF)
- A FF B means "activity A must finish before activity B can finish" (or "B can't finish before A is finished") .[3]
- (Last chapter written) FF (Entire book written)
- A FF B means "activity A must finish before activity B can finish" (or "B can't finish before A is finished") .[3]
- Start to start (SS).
- A SS B means "activity A must start before activity B can start" (or "B can't start until A has started").[3]
- (Project work started) SS (Project management activities started)
- A SS B means "activity A must start before activity B can start" (or "B can't start until A has started").[3]
- Start to finish (SF)
Finish-to-start is considered a "natural dependency". The
SF is rarely used, and should generally be avoided. Microsoft recommends to use SF dependency for just-in-time scheduling.[4] It can be easily shown however, that this would only work if resource levelling is not used, because resource levelling can delay a successor activity (an activity, which shall be finished just-in-time) in such a way, that it will finish later than the start of its logical predecessor activity, thus not fulfilling the just-in-time requirement.
There are three kinds of dependencies with respect to the reason for the existence of dependency:
- Causal (logical)
- It is impossible to edit a text before it is written
- It is illogical to pour concrete before you dig the foundations of a building
- Resource constraints
- It is logically possible to paint four walls in a room simultaneously but there is only one painter
- Discretionary (preferential)
- I want to paint the living room before painting the dining room, although I could do it the other way round, too
Early
Leads and lags
Dependencies can be modified by leads, and lags. Both leads and lags can be applied to all 4 types of dependencies.
For example: When building two walls from a novel design, one might start the second wall 2 days after the first so that the second team can learn from the first. This is an example of a lag in a Start-Start relationship.
In accordance to
Example
If you are building a building, you can't paint the walls before installing the water pipes into the walls.
Advanced cases of activities dependencies
Maximal-type relationships
Activity A and Activity B are said to have a Maximal-Type Relationship, if Activity B can start after Activity A, but with the delay of no more than X.[5] Real life examples, which are simulated by Maximal-Type Relation:
- Shoring of the trench has to be done not necessarily immediately after excavation, but within certain time, otherwise the trench will collapse.
- Vaccination of baby has to be done not immediately after birth, but within certain time
- Renewal of the passport has to be done some time after the current one has been issued, but before it expires.
- Invoice payment does not have to be done immediately, but within certain time after it has been issued.
Maximal-type relationships are rarely implemented in the project management software, most probably because with this feature it is too easy to create contradictory dependencies.
See also
- Dependency structure matrix
- Outline of project management
- Project network
- Project planning
Citations
- ^ ISBN 978-1-935589-67-9.
- ^ Mulcahy 2021, p. 173.
- ^ ISBN 978-1-935589-24-2.
- ^ "Microsoft article of SF links for Microsoft Project". Archived from the original on 2014-02-02.
- ^ "ProJack Manager web site, describing maximal-type relationships". Archived from the original on 2014-02-03.
References
- Mulcahy, Rita (2021). PMP Exam Prep, Tenth Edition-Upgraded. ISBN 1-943704-27-9.