HKSM

A technique to model project activities and their logical relationships as a network of nodes and links. It uses four relationship types and optional leads and lags to sequence work and enable critical path and float analysis.

Definition

This method is commonly drawn as an activity-on-node network, where each box is an activity and arrows show the dependency logic used to build and analyze the schedule.

Key Points

• Represents activities as nodes and logical relationships as directional links.
• Supports four relationship types: finish-to-start (FS), start-to-start (SS), finish-to-finish (FF), and start-to-finish (SF).
• Allows leads and lags to fine-tune timing between linked activities.
• Enables identification of the critical path and calculation of total and free float.
• Distinguishes different dependency origins such as mandatory, discretionary, or external.
• Forms the basis for schedule analysis, what-if scenarios, and updates during change control.

What the Diagram Shows

• All planned activities as nodes with identifiers and durations.
• Logical sequencing through directed links with relationship types and lead/lag values.
• Paths from project start to finish, highlighting the longest path as the critical path.
• Early and late dates and float values when forward and backward passes are performed.
• Converging and diverging logic that may signal risk hotspots or coordination needs.
• External dependencies and constraints that affect start or finish timing.

How to Construct

• List all activities with clear scopes and durations.
• Identify logical dependencies for each activity, including mandatory, discretionary, and external links.
• Select the appropriate relationship type (FS, SS, FF, SF) for each dependency.
• Assign leads or lags where timing overlaps or waits are needed, and document the rationale.
• Draw nodes for activities and connect them with directional links labeled with the relationship and any lead/lag.
• Check the network for completeness, ensuring a single start and finish path without loops.
• Perform forward and backward pass calculations to get early/late dates and float.
• Highlight the critical path and review with the team for feasibility and risks.
• Update the diagram as assumptions change or as part of schedule change control.

Inputs Needed

• Activity list and activity attributes, including durations and predecessors.
• Scope baseline and WBS to confirm completeness and decomposition.
• Milestone list and required delivery dates or windows.
• Assumptions and constraints that influence sequencing or timing.
• Resource calendars and availability that may drive discretionary logic.
• Risk responses that impose leads, lags, or additional checks.
• Agreements or external commitments creating inbound or outbound dependencies.

Outputs Produced

• Schedule network diagram showing nodes, links, and relationship details.
• Predecessor-successor table with relationship types and lead/lag values.
• Calculated early and late dates for activities and milestones.
• Critical path identification and float values for each activity.
• Sequencing rationale and assumptions log to support future changes.
• Updates to the schedule model and data for reporting and baselining.

Interpretation Tips

• Read from left to right to follow logical flow from start to finish.
• Focus on long chains and converging points; they often indicate schedule risk.
• Inspect leads and lags carefully; they can hide risk or create unrealistic overlaps.
• Use float to prioritize monitoring; zero or near-zero float needs closer control.
• Flag external dependencies since they can shift without your control.
• After changes, always recalculate dates and revalidate the critical path.

Example

Consider five activities with durations: A(2), B(3), C(5), D(2), E(1). Relationships: A FS to B and C; B FS to D; C FS+2 to D (a 2-day lag); D FS to E. The A-B-D-E path totals 8 days, while A-C-D-E includes a 2-day lag and totals 12 days. The critical path is A-C-D-E.

Pitfalls

• Overusing SS or FF links when FS would be clearer and easier to control.
• Adding leads or lags without documented reasoning, reducing transparency.
• Ignoring resource limits and calendars, which can invalidate the logic.
• Creating circular dependencies or open ends that break the network.
• Treating discretionary links as mandatory, reducing schedule flexibility.
• Failing to update the network after change requests or risk responses.

PMP Example Question

A project manager wants to model activity sequence using nodes for tasks and links that can be FS, SS, FF, or SF, with the ability to add leads and lags. Which technique should be used?

1. Gantt chart.
2. Precedence diagramming method.
3. To-Complete Performance Index.
4. Monte Carlo simulation.

Correct Answer: B — Precedence diagramming method

Explanation: PDM models activities as nodes with defined relationship types and supports leads and lags, enabling network analysis and critical path determination.