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
It is a Logical Relationship in which a Successor Activity cannot start until a Predecessor Activity has started. In other words, the Start of a Successor is Dependent on Start of the Predecessor.
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.
The Project Team will need a total of 3 days to complete these activities.
Bar Chart Representation
B can Start (S) after A Starts (S)
B(S) = A(S)
Let us consider 2 activities A and B. Let us also consider A to be the Predecessor and B to be the Successor.