Start-to-Start (SS) Dependency
A Start-to-Start (SS) dependency is a logical relationship in which a successor activity cannot start until a predecessor activity has started.
Explanation
Start-to-Start dependencies allow two activities to begin at the same time or with a controlled offset. The successor activity can only start once the predecessor has started, but they do not need to finish together. This type of relationship is useful when two activities can run in parallel but one depends on the other beginning first.
For example, a project might have a coding activity and a documentation activity with an SS relationship. Documentation can begin once coding starts (since the documentation team needs to see some code to document), but the two activities proceed independently after that point. An SS relationship with a lag might specify that documentation starts two days after coding begins.
SS dependencies are less common than FS dependencies but are valuable for modeling concurrent work streams. They are frequently combined with FF (Finish-to-Finish) dependencies to fully constrain the timing between parallel activities, ensuring they both start and finish in a coordinated manner.
Key Points
- •Successor cannot start until predecessor starts
- •Allows parallel execution of activities
- •Often combined with FF dependencies for full constraint
- •Commonly used with lags to offset start times
Exam Tip
SS does not mean both activities start at exactly the same time. It means the successor cannot start until the predecessor has started. A lag can offset the starts.
Frequently Asked Questions
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Precedence Diagramming Method (PDM)
The Precedence Diagramming Method (PDM) is a technique used to construct a schedule model in which activities are represented by nodes and are graphically linked by logical relationships to show the sequence of activities.
Finish-to-Start (FS) Dependency
A Finish-to-Start (FS) dependency is a logical relationship in which a successor activity cannot start until a predecessor activity has finished.
Finish-to-Finish (FF) Dependency
A Finish-to-Finish (FF) dependency is a logical relationship in which a successor activity cannot finish until a predecessor activity has finished.
Leads and Lags
A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time a successor activity must be delayed with respect to a predecessor activity.
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