5.2.1. Scheduling Techniques

💡 First Principle: A work breakdown structure organizes scope by what will be delivered, not by the order work happens in. Sequencing that decomposed work into a schedule — and finding the longest dependent chain through it — is a separate step that comes after the WBS exists, not the same step.

WBS and work packages. The WBS is a deliverable-oriented hierarchical decomposition of total project scope. Each level breaks a deliverable into smaller, more specific deliverables until you reach work packages — pieces small enough to reliably estimate, assign, and track.

⚠️ Exam Trap: A WBS is not a sequential to-do list — it says nothing about order. A scenario listing steps "in the order they'll happen" is describing an activity list or schedule, a different artifact built from the WBS afterward, not the WBS itself.

The critical path method. Once work packages are broken into activities and sequenced with dependencies, the critical path is the longest sequence of dependent activities from start to finish — it determines the shortest possible project duration. Any delay to an activity on the critical path delays the whole project; delays to activities not on the critical path may not, as long as they stay within their available slack.

In this simplified network, Path A→C totals 7 days and Path B→D totals 3 days. A→C is the critical path (shown in red) — it's the longest chain, so it sets the project's minimum duration at 7 days, even though it's made of only two activities, not the most activities.

⚠️ Exam Trap: The critical path is a path — a chain of linked activities — not the single longest individual activity in the project. A scenario asking "which activity takes the longest" is a different question from "which path is critical," and they can have different answers depending on how activities are sequenced.

Why slack determines where monitoring attention goes. A path with zero slack — where any delay directly extends the whole project — deserves closer, more frequent monitoring than a path with several days of slack absorbing the same size delay without consequence. This is more than a definitional point: given limited attention, an associate-level practitioner is expected to recognize that not every path warrants equal scrutiny, and prioritizing the zero-slack path over one with a healthy buffer is the practical payoff of understanding what slack actually measures. A project can also legitimately have more than one critical path at once, if two or more paths tie for the longest duration — in that case, all of the tied paths are critical simultaneously, not just the first one identified, and each deserves the same monitoring priority.

Introducing schedule variance. Once a schedule is baselined, Schedule Variance (SV) measures whether work is ahead of or behind that baseline. The full formula and its cost-side counterpart are covered together in 5.3, where both are used as ongoing control tools rather than one-time scheduling calculations.