Scheduling, activities, dependencies and resource allocation
Scheduling and dependencies
Scheduling starts with an activity list, estimates of duration and resources, and sequencing. Precedence diagrams show dependencies: finish-to-start (most common), start-to-start, finish-to-finish and start-to-finish, with lead or lag where needed. Classify dependencies as mandatory, discretionary or external. Distinguish effort from duration: two people may finish a task in half the effort-time only if the work is divisible; adding people can add coordination overhead. Milestones have zero duration and mark significant points.
The critical path is the longest path through the network and determines the shortest possible project duration. Activities on it have zero float (slack); delay there delays the project. Float on other paths is a buffer, not free time to ignore. Resource overallocation is handled by resource leveling (which may change the critical path and finish date) or resource smoothing (which protects the end date within float). Crashing adds cost/resources; fast tracking overlaps phases and increases risk.
Traps
A frequent error is choosing the shortest path as critical. Another is assuming the critical path never changes-leveling, changes or delays can shift it. Duration and effort are often swapped in questions. Do not treat every dependency as mandatory; discretionary dependencies can sometimes be removed. A Gantt chart is a view, not the schedule logic itself.
Worked example
Activities: A (3 days) precedes B (4) and C (2); B and C both precede D (2). Path A–B–D takes 9 days; A–C–D takes 7. The critical path is A–B–D, project duration 9 days, and C has 2 days of float. If B is delayed one day, the project moves to 10 days unless float elsewhere is used. Rule: perform a forward pass for early dates and a backward pass for late dates; the zero-float path is critical.