In this article, you will find explanation of Start to Finish logical relationship in project management with examples and diagrams. It provides visual depiction of the relationship using Project Network Diagrams and Gantt Charts.
Start to Finish Relationship (Dependency) in Project Management
An activity relationship is loosely termed as project dependency. However, these two are different. A relationship between two activities can be established only if one activity is dependent on the other.
Start to Finish (SF) is one of the four relationships that are used to prepare a project schedule. The other three are:
Note: There are four types of dependencies, which are different from the four relationships of the project management.
Definition of SF Relationship
As per the PMBOK Guide “Start To Finish is a Logical Relationship in which a Successor Activity cannot finish until a Predecessor Activity has started”.
However a better definition is, “Start to Finish is a Logical Relationship in which finishing event of a Successor Activity is dependent on the starting event of a Predecessor Activity”.
To understand the definition further, let us look at the activity events and not at activity as a whole. The two distinct events of any activity are:
- Start Event (S)
- Finish Event (F)
In SF relationship, the Finish of Second Activity is dependent on the Start of First Activity. The Second Activity is called the Successor and the First Activity is called the Predecessor.
You can also look at Max Wideman’s Glossary for a complete set of PDM definitions.
Start To Finish Examples
Let us consider two activities X and Y. X and Y are predecessor and successor activities respectively. The following examples show FS relationship between X and Y:
- X – Duty of Evening Guard (E), Y – Duty of Morning Guard (M). M cannot Finish her/his duty till E Starts. Simple speaking M cannot abandon the post even if E gets delayed.
- X – Start using New Software System (N), Y – Phase out Old Software System (O). It is assumed that N & O cannot be used in parallel. O cannot be phased out until N is started.
Gantt Chart Representation
An FS relationship can be visually depicted using using Time Scaled Bar Charts, which are popularly known as Gantt Charts.
Let us consider two activities A and B.
- Duration of A is 3 days.
- Duration of B is 1 day.
- B has a SF relationship with A
The Gantt Chart below shows SF relationship between A and B.
As per the above diagram B’s Finish is dependent on A’s Start, which means that B can Finish(F) as soon as A Starts(S).
In the above example, A and B together are scheduled to be completed in 4 days.
Project Network Diagram Representation
An FS relationship can also be drawn by using Precedence Diagramming Method (PDM), which can be visually depicted by Project Network Diagrams.
Let us again consider the above two activities A and B. The Network Diagram below shows SF relationship between A and B.
Mathematical Representation And Formulas
Again considering the above two activities A and B and using 0 method, we can mathematically represent the relationship between A and B as:
B(F) = A(S)
Or, if we use 1 method, we can say that:
B(F) = A(S) – 1
Start to Finish with Lead and Lag
SF relationships can be further modified by introducing Lead and Lag modifiers.
The following Lead and Lag examples use 0 method representation.
Two activities J and K having FS relationship with 1 day of Lead:
K(F) = J(S) – 1 day
Two activities L and M having FS relationship with 2 days of Lag:
M(F) = L(S) + 2 days
Finish to Start is Different from Start to Finish
SF is not a very difficult concept to understand but sometimes it is confused with Finish to Start (FS) relationship. Some authors (incorrectly) claim that FS and SF are essentially same but it is not true.
FS is the most common and natural relationship but it cannot represent every sequence of activities. Although SF can be mathematically transformed to FS to achieve seemingly similar results, the mathematical transformation modifies and tampers the natural logic.
Let’s revisit the Guard example from the previous section to understand why SF is more natural than FS. In the above example, there were two Guards who are doing a shift duty – Evening Guard (E) and Morning Guard (M).
In a natural scenario, M can “Finish” her/his duty only “only after” E “Starts” his/her duty. The critical point here is that “M cannot Finish her/his duty even one minute before E Starts”, otherwise it will be tantamount to abandoning the post. Since M cannot abandon the post, she/he has to guard the post even if E gets delayed in starting her/his duty.
The Finish of M is logically dependent on Start of E.
Over to You
PDM Relationships are logical relationships that can be represented by using mathematical equations. However, not all mathematical relationships represent the natural logic. While making a project schedule, you should ensure that all dependencies follow the natural logic and are true in the real world.
Do you think SF relationship is useful in real projects? Have you ever used it in you project(s)? Or have you seen it being used?
I would love to hear from you.
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