Q 362. What are the 4 types of Logical Relationships (or task dependencies) in project management? Provide a suitable example for each of the relationships.

 

 

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4 Logical Relationships in a Project Management

Logical Relationships or Task dependencies, denotes the start and finish time (or dates) of a task as it is connected to other activities. The relations are known as :

i) Finish-to-Start (FS),

ii) Start-to-Start (SS),

iii) Finish-to-Finish  (FF),

iv) Start-to-Finish (SF).

Each relationship behaves differently as successors & predecessors interaction.

Activities of Predecessor: The planned activity which determines when the logical successor activity could begin or end.

Activities of Successor: The planned activity that follows a predecessor activity, as determined by the logical relationship.

Finish-to-Start (FS)

It simply means; once a task is finished, we are allowed to start the next task.

In other words, the Predecessor’s finish time or date determines the Successor’s start time or date.

(Fig 1)

Start-to-Start (SS)

It simply means; these 2 tasks need to start at the same  time

In other words; when the predecessor task starts,  the successor task should also start.

(Fig 2)

Finish-to-Finish (FF)

It simply means;  2 tasks are required to finish at the same time

In other words;  the successor task must finish once the predecessor task finishes.

(Fig 3)

Start-to-Finish (SF)

It simply means; Task B finishes whenTask A starts, but not before that.

In other words; once the successor task finishes, only then the predecessor task should start.

(Fig 4)

4 Types of logical relationships:
1.   Finish to Start
2.  Start to Start
3.  Finish to Finish
4.  Start to Finish

 

Finish to Start: 
A logical connection in which a next-in-line cannot start until a forerunner activity has finished.
This relation constraint doesn’t impact the independent activity. It affects only the dependent, so in the below case, it is activity B.

The first character ‘F’ shows the finish state of activity A, at this state, activity B can started. The second character ‘S’ is the rule on the next step to make it dependent on the Finish state of the successor activity.
Example:
You cannot start next stage until you finish the design. In this case, development is the dependent activity on the design activity.

Start to Start:
A logical relationship in which a next-in-line activity cannot start until a forerunner activity has started.

So if activity B is leap to this relation, which means it cannot start till the forerunner (independent) activity A is started.

 

The forerunner activity B start is dependent on the start state of next-in-line activity A. The start of activity A operate the start of activity B.
Example:
The activity of marketing booklet preparation cannot start until user manual documentation has begun. In this way, after the opening of activity A, both A and B will can go in parallel.

 

Finish to Finish:
A logical relationship in which a next-in-line activity cannot finish until a forerunner activity has finished.”
So if activity B is leap with this relation, which means it cannot finish till the forerunner (independent) activity A is finished. So, B needs to finish the deliverable and parallelly keep working with A till the time A is not completed.

 

Example:
Like, the telecast of a cricket match cannot finish until the match is finished. So the match is not depended in telecast, but the telecast is. If the match will take longer than the initially planned time the telecast will also continue till that time..

 

Start to Finish:
“A logical connection in which a next-in-line activity cannot finish until a forerunner activity has started.”

So if activity B is leap to this relation, which it cannot finish till the independent activity A starts. It looks bit confusing because in some cases, forerunner activity gets performed before the next-in-line activity. But, in this case, the next-in-line is happening first. But even if the next-in-line is happening first, the forerunner is not at all restricted by next-in-line activity. 

 

In Project management, after identification of activities, we analyze them if any relationships exist between those. If relationships exist, it is better to highlight them in Project Schedule Network Diagrams to maintain the project schedule better.

 

There are four (4) types of dependency relationships. Taking an example of building a house on a piece of land :

 

1) Finish to Start : Predecessor must finish before Successor can start. (Example : Land must be purchased before house building can start)

 

2) Start to Start : Predecessor must start before Successor can start. (Example : Land digging must start before House foundation can be laid)

 

3) Finish to Finish : Predecessor must finish before Successor can finish. (Example : Laying Cement must be complete before final Painting can be completed)

 

4) Start to Finish : Predecessor must start before Successor can finish. (Example : Whitewashing must start before final painting can be completed)

 

All the published answers have correctly explained the 4 logical relationships. However these had to be supported with examples as well and hence there are two winners for this question - Suresh Sekar and Dipankar Acharya.