Scheduling Fundamentals
Relationship Types (FS, SS, FF, SF)
Relationship types define how one activity depends on another: Finish-to-Start, Start-to-Start, Finish-to-Finish, and Start-to-Finish, each linking the two activities' dates differently.
Definition
Finish-to-Start (FS) is the default and most common relationship: the successor can't start until the predecessor finishes. Start-to-Start (SS) ties the two activities' start dates instead, letting the successor begin once the predecessor has started (optionally with a lag). Finish-to-Finish (FF) ties their finish dates. Start-to-Finish (SF) is rare and usually signals a modeling mistake rather than a deliberate choice. DCMA's target distribution is FS at 90% or more of all logic, SS and FF combined under 10%, and SF at zero. This isn't a cosmetic preference -- heavy reliance on SS/FF logic is one of the most common ways a schedule gets artificially compressed: downstream work is allowed to 'start' without the predecessor actually being finished, so the finish date holds even though the underlying sequence no longer reflects how the work will really happen. Checking the FS/SS/FF/SF mix is often the first thing worth doing before trusting a schedule's forecast at all.
Example
A schedule shows 'Install Drywall' tied to 'Rough-In Electrical' with a Start-to-Start relationship instead of the more typical Finish-to-Start -- meaning drywall is scheduled to begin as soon as electrical rough-in starts, not after it's actually complete, which may not reflect how the trades can really sequence on site.