PDM Relationships – Start to Start
This article extends my previous article on Project Network Diagram. Project Network Diagrams are used to pictorially represent Project Schedule and Project Dependencies. You can also read my other articles on Project Dependencies – What are Project Dependencies and 4 Types of Project Dependencies.
There are many ways to draw a Project Network Diagram. One of them is Precedence Diagramming Method (PDM). PDM defines 4 Logical Relationships to represent Project Dependencies. This post to describes Start to Start (SS) Relationship. Start to Start is one of the 4 Logical Relationships. The other 3 Logical Relationships are Finish to Start, Finish to Finish and Start to Finish.
Definition of Start to Start Relationship
Start to Start is a Logical Relationship in which a Successor Activity cannot start until a Predecessor Activity has started.
In simple words we can say that, the Start of a Successor Activity is Dependent on Start of the Predecessor Activity.
Most Project Management Authors treat above definition of SS Relationship as standard. However, some Scheduling Software treat SS Relationship slightly differently. They treat SS Relationship as “Must Start Together” Relationship. So, if one one of the activities Starts other is Automatically Started.
The most common and most natural relationship is Finish to Start (FS). Start to Start Relationship is sometimes used. The Project Managers have some flexibility while defining the relationship between 2 activities. Usually it is possible for them to transform a SS Relationship to a FS Relationship.
You can also look at Max Wideman’s Glossary for complete set of definitions on PDM Logical Relationships.
Project Network Diagram Representation
Let us consider two activities A and B.
- Duration of A – 3 days
- Duration of B – 1 day
- B has a Start to Start Relationship with A – B cannot Start until A Starts
In the above example, the Project Team will need a total of 3 days to complete these activities.
Bar Chart Representation
Mathematical Representation And Formulas
For both 0 method and 1 method
B(S) = A(S)
Start to Start Examples
Let us consider 2 activities A and B. Let us also consider A to be the Predecessor and B to be the Successor.
- A – Write Code for S/W Module X, B – Write DB Scripts for S/W Module X
- A – Pour Asphalt, B – Level Road
- A – Write User Manual, B – Review User Manual
Over To You
Do you think this is useful in real projects? Have you ever used it in you project(s)?
Please leave a comment.
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