roadmap-backcast（路线图回溯）

Roadmap Backcast

Table of Contents

1. Workflow
2. Dependency Mapping
3. Critical Path Analysis
4. Common Patterns
5. Guardrails
6. Quick Reference

Workflow

Copy this checklist and track your progress:

Roadmap Backcast Progress:
- [ ] Step 1: Define target outcome precisely
- [ ] Step 2: Work backward to identify milestones
- [ ] Step 3: Map dependencies and sequencing
- [ ] Step 4: Identify critical path
- [ ] Step 5: Assess feasibility and adjust

Step 1: Define target outcome precisely

State specific outcome (not vague goal), target date, success criteria. See Common Patterns for outcome definition examples. For straightforward backcasts → Use resources/template.md.

Step 2: Work backward to identify milestones

Start at end, ask "what must be true just before this?" iteratively. Create 5-10 major milestones. For complex multi-year roadmaps → Study resources/methodology.md.

Step 3: Map dependencies and sequencing

Identify what depends on what, what can run in parallel. See Dependency Mapping for techniques.

Step 4: Identify critical path

Find longest sequence of dependent tasks (this determines minimum timeline). See Critical Path Analysis.

Step 5: Assess feasibility and adjust

Compare required timeline to available time. Add buffers (20-30%), identify risks, adjust scope or date if needed. Self-check using resources/evaluators/rubric_roadmap_backcast.json before finalizing. Minimum standard: Average score ≥ 3.5.

Dependency Mapping

Dependency types:

Sequential (A → B): B cannot start until A completes

• Example: Design must complete before engineering starts
• Critical path impact: Extends timeline
• Mitigation: Start A as early as possible, parallelize where safe

Parallel (A ∥ B): A and B can happen simultaneously

• Example: Backend and frontend development
• Critical path impact: None (if resourced)
• Benefit: Reduces overall timeline

Converging (A, B → C): C requires both A and B to complete

• Example: Testing requires both code complete AND test environment ready
• Critical path impact: C waits for slower of A or B
• Mitigation: Monitor both paths, accelerate slower one

Diverging (A → B, C): A enables both B and C

• Example: API contract defined enables frontend AND backend work
• Critical path impact: Delays in A delay everything downstream
• Mitigation: Prioritize A, ensure high quality to avoid rework

Critical Path Analysis

Critical path: Longest sequence of dependent tasks (determines minimum project duration)

Finding critical path:

1. List all milestones with durations
2. Draw dependency graph (arrows from prerequisite to dependent)
3. Calculate earliest start/finish for each milestone (forward pass)
4. Calculate latest start/finish for each milestone (backward pass)
5. Milestones with zero slack (earliest = latest) are on critical path

Example:

Milestone A (4 weeks) → Milestone B (6 weeks) → Milestone D (2 weeks) = 12 weeks (critical path)
Milestone A (4 weeks) → Milestone C (3 weeks) → Milestone D (2 weeks) = 9 weeks (non-critical, 3 weeks slack)

Critical path is 12 weeks (A→B→D path)

Managing critical path:

• Monitor closely: Delays on critical path directly delay project
• Add buffer: 20-30% to critical path tasks (Murphy's Law)
• Resource priority: Staff critical path first
• Fast-track: Can non-critical work be delayed to help critical path?
• Crash: Add resources to shorten critical path (diminishing returns, Brook's Law applies)

Common Patterns

Pattern 1: Product Launch with Fixed Date

• Target: Product live by date, serving customers
• Key milestones (backward): GA launch, beta testing, feature freeze, alpha testing, MVP, design complete, requirements locked
• Critical path: Usually design → engineering → testing (sequential)
• Buffer: 20-30% on engineering (unknowns), 20% on testing (bugs)

Pattern 2: Compliance Deadline (Regulatory)

• Target: Compliant by regulatory deadline (cannot slip)
• Key milestones: Audit passed, controls implemented, policies updated, gap analysis complete
• Critical path: Gap analysis → remediation → validation
• Buffer: 40%+ (regulatory risk intolerant, build extra time)

Pattern 3: Strategic Transformation (Multi-Year)

• Target: Future state vision (e.g., "Cloud-native architecture by 2027")
• Key milestones (annual): Year 3 (full migration), Year 2 (50% migrated), Year 1 (pilot complete), Year 0 (strategy approved)
• Critical path: Foundation work (pilot, learnings) enables scale
• Buffer: 30%+ per phase (unknowns compound over time)

Pattern 4: Event Planning (Conference, Launch Event)

• Target: Event happens on date, attendees have great experience
• Key milestones: Event day, rehearsal, content ready, speakers confirmed, venue booked, date announced
• Critical path: Venue booking (long lead time) often on critical path
• Buffer: 10-20% (events have hard deadlines, less flexible)

Guardrails

Feasibility checks:

• Available time ≥ required time: If backward timeline reaches before today, goal is infeasible
• Buffer included: Add 20-30% to estimates (Hofstadter's Law: "It always takes longer than you expect, even when you account for Hofstadter's Law")
• Dependencies realistic: Can dependent work actually be done in sequence (handoff time, rework)?
• Resource constraints: Do we have people/budget to parallelize where needed?

Common pitfalls:

• Optimistic sequencing: Assuming perfect handoffs, no rework, no blockers
• Ignoring dependencies: "We can start everything at once" → actually highly sequential
• No buffer: Plans with 0% slack fail on first hiccup
• Scope creep: Target outcome expands during execution, invalidates backcast
• Sunk cost fallacy: When backcast shows infeasibility, adjust scope or date (don't plow ahead)

Quality standards:

• Milestones have clear deliverables (not "working on X")
• Dependencies explicitly mapped (not assumed)
• Critical path identified (know what determines timeline)
• Feasibility assessed honestly (not wishful thinking)
• Risks documented (what could extend timeline?)
• Owners assigned to each milestone (accountability)

Quick Reference

Resources:

• Quick backcast: resources/template.md
• Complex roadmaps: resources/methodology.md
• Quality rubric: resources/evaluators/rubric_roadmap_backcast.json

5-Step Process: Define Target → Work Backward → Map Dependencies → Find Critical Path → Assess Feasibility

Dependency types: Sequential (A→B) | Parallel (A∥B) | Converging (A,B→C) | Diverging (A→B,C)

Critical path: Longest dependent sequence = minimum project duration

Buffer rule: Add 20-30% to estimates, 40%+ for high-uncertainty work

Feasibility test: Required time ≤ Available time (with buffer)