requirements-flowdown

Requirements Flow-Down Skill

Purpose

The Requirements Flow-Down skill provides systematic capabilities for capturing, decomposing, and tracing requirements throughout the mechanical design process, ensuring design intent is properly communicated and verified.

Capabilities

• Stakeholder requirements elicitation
• Functional requirements decomposition
• Performance requirements specification
• Design constraint identification
• Requirements traceability matrix
• Verification method assignment
• Requirements change management
• Code and standard flow-down

Usage Guidelines

Requirements Hierarchy

Requirements Levels

Level 1: Stakeholder Requirements
- What the customer/user needs
- High-level, solution-independent
- Source: Customer specifications, standards

Level 2: System Requirements
- What the system must do
- Allocated from stakeholder requirements
- Source: System engineering

Level 3: Subsystem Requirements
- What each subsystem must do
- Allocated from system requirements
- Source: Architecture trade studies

Level 4: Component Requirements
- What each component must do
- Allocated from subsystem requirements
- Source: Detailed design

Requirement Types

| Type | Description | Example |

|------|-------------|---------|

| Functional | What the system does | "Shall lift 500 kg" |

| Performance | How well it performs | "Lifting time < 30 sec" |

| Interface | Connections to other systems | "Shall mate with Type A connector" |

| Environmental | Operating conditions | "Shall operate at -40 to +85 C" |

| Physical | Size, weight, shape | "Shall weigh < 25 kg" |

| Reliability | Failure characteristics | "MTBF > 10,000 hours" |

| Maintainability | Service characteristics | "Shall be serviceable in field" |

| Safety | Hazard prevention | "Shall prevent pinch points" |

Requirements Development

Requirements Attributes

Each requirement should have:
- Unique identifier (REQ-XXX-XXXX)
- Requirement text (shall statement)
- Rationale (why needed)
- Source (parent requirement or stakeholder)
- Priority (must have, should have, nice to have)
- Verification method (analysis, test, inspection, demo)
- Owner (responsible engineer)
- Status (draft, approved, verified)

Well-Written Requirements

Good requirement characteristics (SMART):
- Specific: Unambiguous and clear
- Measurable: Quantifiable acceptance criteria
- Achievable: Technically feasible
- Relevant: Traces to stakeholder need
- Traceable: Links up and down hierarchy

Bad: "The system shall be easy to use"
Good: "The system shall be operable by one person
      without tools within 5 minutes of training"

Requirements Decomposition

Decomposition Process

1. Parse Parent Requirement

• Identify measurable parameters
• Identify applicable conditions
• Identify affected components

1. Allocate to Children

• Assign parameters to subsystems
• Maintain budget (sum of allocations)
• Document allocation rationale

1. Derive Supporting Requirements

• Interface requirements
• Enabling requirements
• Constraint requirements

Budget Allocation Example

Parent: "System shall weigh < 100 kg"

Children:
- Structure: < 40 kg (40%)
- Mechanism: < 25 kg (25%)
- Electronics: < 15 kg (15%)
- Cabling: < 10 kg (10%)
- Margin: 10 kg (10%)

Traceability Matrix

Matrix Structure

Requirements Verification Matrix (RVM):

| Req ID | Requirement Text | Source | Verification Method | Evidence |
|--------|------------------|--------|---------------------|----------|
| REQ-001 | Shall lift 500 kg | SRS-001 | Test | Test Report TR-001 |
| REQ-002 | Shall operate at -40C | SRS-002 | Test | Test Report TR-002 |
| REQ-003 | Shall weigh < 25 kg | SRS-003 | Inspection | FAI-001 |

Verification Methods

| Method | Application | Evidence |

|--------|-------------|----------|

| Analysis | Calculations, simulations | Analysis report |

| Test | Physical testing | Test report |

| Inspection | Visual/dimensional check | Inspection report |

| Demonstration | Functional demo | Demo record |

Code and Standard Flow-Down

Standards Application

Mechanical standards flow-down:
1. Identify applicable standards (contract, regulatory)
2. Extract applicable requirements from standards
3. Create derived requirements with standard reference
4. Track compliance through verification

Common Standard Sources

| Domain | Standards |

|--------|-----------|

| Structural | ASME BPVC, AWS D1.1, AISC |

| Materials | ASTM, SAE AMS, MMPDS |

| Drawing | ASME Y14.5, ASME Y14.100 |

| Quality | ISO 9001, AS9100 |

| Safety | OSHA, ANSI, ISO 13849 |

| Environmental | MIL-STD-810, IEC 60068 |

Requirements Change Control

Change Process

1. Change request submitted
2. Impact assessment
   - Technical impact
   - Cost impact
   - Schedule impact
   - Downstream requirements
3. Review and approval
4. Implementation
5. Verification of change
6. Update traceability

Process Integration

• ME-001: Requirements Analysis and Flow-Down

Input Schema

{
  "source_documents": {
    "customer_spec": "string",
    "applicable_standards": "array",
    "interface_documents": "array"
  },
  "system_context": {
    "system_name": "string",
    "subsystems": "array",
    "interfaces": "array"
  },
  "requirement_level": "stakeholder|system|subsystem|component"
}

Output Schema

{
  "requirements_set": [
    {
      "id": "string",
      "text": "string",
      "type": "functional|performance|interface|environmental|physical",
      "source": "string",
      "parent": "string",
      "verification_method": "analysis|test|inspection|demonstration",
      "owner": "string",
      "priority": "must|should|nice",
      "status": "draft|approved|verified"
    }
  ],
  "traceability_matrix": {
    "upward": "matrix of parent links",
    "downward": "matrix of child links",
    "verification": "matrix of evidence links"
  },
  "budgets": {
    "mass": "object of allocations",
    "power": "object of allocations",
    "cost": "object of allocations"
  },
  "open_items": "array of TBD/TBR items"
}

Best Practices

1. Write requirements in shall statements
2. Each requirement should be verifiable
3. Maintain clear parent-child traceability
4. Review requirements with stakeholders
5. Control changes through formal process
6. Update verification evidence as completed

Integration Points

• Connects with Trade Study for requirement derivation
• Feeds into Design Review for verification
• Supports Test Planning for verification activities
• Integrates with Change Management for requirement changes