Logical Sequencing
The sequential dependency links between activities may be classified into following four types (see Fig. 2):
a) Finish to start (FS) — Successor activity to start after the predecessor activity finishes.
b) Start to start (SS) — Successor activity to start after the predecessor activity has started and is partially complete. So, for some duration both the activities shall take place simultaneously.
c) Finish to finish (FF) — Successor activity to finish only after the predecessor activity has finished. In this situation also for some duration both the activities shall take place simultaneously.
d) Start to finish (SF) — There is a relationship between the start of the predecessor activity and the finishing of the successor activity.
Leads and lags define the exact time difference between the two components of any dependency link and shall be identified by the project team members who are aware of the project details. Lead shall indicate the acceleration of the successor activity with respect to the predecessor activity. Lag shall show the delay between the dependency component of a successor activity with respect to that of the predecessor activity.