Activity Sequencing, Durations, and Logic Relationships
This domain examines dependency types, logic attributes, and duration estimating. CAPES expects you to choose the correct relationship, justify lags and leads, distinguish mandatory from discretionary logic, and build durations from documented bases rather than judgment alone. It also tests how calendars and productivity assumptions alter duration.
Dependency types and attributes
- Finish-to-Start (FS) is the default: the successor cannot start until the predecessor finishes.
- Start-to-Start (SS) allows overlap; a lag sets the minimum delay between starts. Finish-to-Finish (FF) ties completion; Start-to-Finish (SF) is rare and usually indicates a flawed model.
- Mandatory logic is contractually or physically required; discretionary logic is a chosen practice and should be documented. External dependencies involve parties outside the project.
- A lag is waiting time or a required interval; a lead is a negative lag. Both should have a stated reason. A lag used to hide unfinished work corrupts the logic.
Duration estimating
Analogous estimating uses historical similarity; parametric estimating uses a rate per unit; three-point estimating uses optimistic, most likely, and pessimistic values. Productivity rates must match the calendar and crew assumptions. A duration should exclude contingency unless the activity is explicitly risk-adjusted.
Worked example
An activity has optimistic = 5 days, most likely = 8 days, pessimistic = 17 days. PERT expected duration = (5 + 4×8 + 17) / 6 = 54 / 6 = 9 days. Standard deviation = (17 − 5) / 6 = 2 days. A bid at 9 days has roughly 50% confidence under the PERT distribution; a more conservative commitment would use a higher percentile. If the crew works a 5-day calendar but the estimate was built on a 7-day calendar, the duration must be converted before it enters the schedule.
Traps that cost marks
Using SF because it seems convenient; inserting lags to avoid detailing work; padding every duration with hidden contingency; and mixing calendar bases. Also watch for SS relationships that allow a successor to finish before its predecessor, which is logically impossible in most construction sequences.