SKIL90004 Chap.3 Networks and Critical Paths
Networks and Critical Paths
A credible schedule comes from work decomposition, durations and real dependencies. This chapter builds precedence networks, compares complete paths, respects merge points and identifies the critical path that controls the earliest finish. It also treats float as conditional scheduling flexibility, explains why criticality can move and connects recovery options with cost, quality and risk trade-offs.
Network arrows should represent technical, approval or resource facts rather than a preferred calendar appearance. At a merge, the later predecessor controls the successor start, so parallel branches are never averaged. A delay may consume float without moving the finish, or may create a new controlling path. Approved recovery must therefore be recalculated and documented instead of assumed from the original network.
What this chapter covers
- 01
Work breakdown structures
- 02
Activity decomposition
- 03
Precedence relationships
- 04
Forward path calculation
- 05
Critical path
- 06
Total float
- 07
Merge logic
- 08
Schedule recovery
Worked example · free
Find a controlling network branch
- 1A plus B reaches the split after six days.
- 1The C branch reaches the merge on day twelve.
- 1The D branch reaches the merge on day nine.
- 1E finishes on day fourteen; D has three days of float in this network.
Key terms
- Work breakdown structure
- A Work breakdown structure decomposes project scope into manageable deliverable-oriented components.
- Precedence relationship
- A Precedence relationship states the required ordering between activities.
- Critical path
- The Critical path is the longest valid path through the current network and controls earliest finish.
- Merge point
- A Merge point requires all relevant predecessor conditions before the successor can proceed.
- Total float
- Total float is the allowable scheduling movement before the current project finish is affected.
- Resource dependency
- A Resource dependency sequences work because the same limited capability is needed in more than one place.
Networks and Critical Paths FAQ
Is the most important task always critical?
No. Criticality is a timing property created by network logic. A visible or expensive task can have float, while a routine approval can control the finish if every controlling path passes through it.
How do I calculate a project duration?
Add durations along every valid complete path, respect splits and merges, and identify the longest path. At a merge, use the later predecessor finish because the successor waits for all required inputs.
What happens when float is used?
The activity may remain non-critical while its scheduling margin shrinks. Once delay exceeds the available float, the finish or critical path changes and the network must be recalculated.
Exam move
Draw small networks from activity tables and narrate every arrow. Calculate each complete path independently, then check merge points and units. Practise explaining why a proposed recovery works and what new cost, coordination, quality or risk exposure it creates. Recompute the network after approved changes because the controlling path is dynamic.
Start with six to eight original activities drawn from a small research workflow. Give each activity one clear completion condition and one duration unit. Build the network without dates first, because logic should come from technical, approval or resource relationships rather than the calendar appearance you want. Challenge every arrow by asking what fact prevents the successor from starting earlier.
Remove links that merely repeat the order in which someone happened to write the list. Perform a path check and a merge check before arithmetic. At every merge, identify the later predecessor. Add durations along complete paths, mark the longest current path and explain criticality as timing rather than importance. Create a shorter parallel branch and compute its margin against the controlling path.
Then introduce a delay smaller than the margin, equal to it and larger than it. Recalculate rather than relying on intuition, and state when the critical path changes or ties. Practise a recovery question with three options: moving non-critical work within float, adding a genuinely qualified resource and reducing optional scope.
For each option, describe what feature changes and what cost, coordination, quality or risk exposure follows. Fast tracking can increase rework; crashing can add cost; scope reduction changes deliverables. Preserve the accepted baseline and record approved structural changes so later variance remains interpretable. In a written answer, show path labels, arithmetic and units. Do not average parallel branches at a merge.
Do not call a visible task critical without network evidence. If a duration is uncertain, name the basis and next evidence point. End the response with the affected milestone, remaining margin and decision required, which turns schedule calculation into control. Add a deliberate resource conflict to the finished network. Decide whether the resulting sequence reflects a physical prerequisite or merely one person's availability.
This distinction determines the recovery choices. Redraw the model after resolving the conflict and check whether a formerly non-critical branch now controls the finish. Explain the change in words before updating the software schedule.
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