# Requirements Traceability - Deep Dive: Regulatory Compliance

## Overview

This document explores requirements traceability in **highly regulated industries** where compliance is mandatory and traceability is a legal requirement.

## Safety-Critical Standards

### DO-178C (Aerospace Software)
**Domain**: Avionics, flight control systems, aerospace

**Key Requirements**:
- **Bidirectional traceability**: High-level → low-level requirements → code → tests
- **Structural coverage analysis**: Statement, decision, MC/DC coverage
- **Traceability matrix**: Required for DAL A/B/C/D certification
- **Tool qualification**: Development tools must be qualified

**Traceability Levels**:
- System requirements → Software requirements
- Software requirements → Design
- Design → Source code
- Source code → Object code
- Requirements → Test cases
- Test cases → Test results

**RTM System Requirements**:
```
- Bidirectional links at all levels
- Coverage metrics (statement, branch, MC/DC)
- Change impact analysis
- Tool qualification data
- Audit trail for certification
```

### ISO 26262 (Automotive Functional Safety)
**Domain**: Automotive, ADAS, autonomous vehicles

**Key Requirements**:
- **ASIL levels**: A (lowest) to D (highest) safety integrity
- **V-Model traceability**: Requirements → Design → Implementation → Testing
- **Safety requirements**: Functional safety requirements must be traceable
- **Verification and validation**: Complete traceability to test cases

**Traceability Requirements by ASIL**:
- **ASIL D**: 100% bidirectional traceability, formal verification
- **ASIL C**: Bidirectional traceability, semi-formal verification
- **ASIL B**: Forward traceability, structured verification
- **ASIL A**: Basic traceability

**RTM System Requirements**:
```
- ASIL-level tagging
- Safety requirement classification
- Hazard analysis links
- Verification method tracking
- Change impact on safety
```

### IEC 62304 (Medical Device Software)
**Domain**: Medical devices, healthcare software

**Key Requirements**:
- **Software safety classification**: A (low), B (medium), C (high)
- **Traceability**: Requirements → Architecture → Design → Code → Tests
- **Risk management**: ISO 14971 integration
- **Change control**: 21 CFR Part 11 compliance

**Traceability Requirements**:
- System requirements → Software requirements
- Software requirements → Software architecture
- Software architecture → Detailed design
- Detailed design → Implementation
- Requirements → Verification activities
- Requirements → Risk controls

**RTM System Requirements**:
```
- Safety classification tracking
- Risk control linkage
- Verification method documentation
- Change history with rationale
- Electronic signature support (21 CFR Part 11)
```

### IEC 61508 (Functional Safety)
**Domain**: Industrial automation, process control

**Key Requirements**:
- **SIL levels**: 1 (lowest) to 4 (highest) safety integrity
- **Safety lifecycle**: Concept → Realization → Operation → Decommissioning
- **Systematic capability**: Tool qualification requirements
- **Traceability**: All lifecycle phases

**RTM System Requirements**:
```
- SIL-level tracking
- Lifecycle phase management
- Tool qualification data
- Systematic failure analysis
- Probabilistic failure analysis
```

## Regulatory Frameworks

### FDA 21 CFR Part 11 (Electronic Records)
**Domain**: Pharmaceutical, medical devices, clinical trials

**Key Requirements**:
- **Electronic signatures**: Legally binding
- **Audit trails**: Complete, immutable, timestamped
- **System validation**: IQ/OQ/PQ documentation
- **Access control**: Role-based permissions

**RTM System Requirements**:
```
- Immutable audit trail
- Electronic signature support
- User authentication and authorization
- Change control with approval workflow
- System validation documentation
- Backup and recovery procedures
```

### GDPR/Privacy Compliance
**Domain**: Data protection, privacy

**Key Requirements**:
- **Data lineage**: Track data from source to use
- **Right to erasure**: Ability to delete all user data
- **Consent management**: Track consent for data processing
- **Data minimization**: Justify data collection

**RTM System Requirements**:
```
- Data lineage tracking
- Consent requirement links
- Privacy impact assessment links
- Data retention policy enforcement
- Deletion verification
```

## Compliance Patterns

### Pattern 1: V-Model Traceability
```
System Requirements
    ↓ (decomposes_to)
Software Requirements
    ↓ (decomposes_to)
Architecture Design
    ↓ (decomposes_to)
Detailed Design
    ↓ (implements)
Implementation
    ↑ (validates)
Unit Tests
    ↑ (validates)
Integration Tests
    ↑ (validates)
System Tests
    ↑ (validates)
Acceptance Tests
```

### Pattern 2: Risk-Based Traceability
```
Hazard Analysis
    ↓ (identifies)
Safety Requirements
    ↓ (mitigates)
Risk Controls
    ↓ (implements)
Design Elements
    ↓ (validates)
Verification Activities
    ↓ (confirms)
Residual Risk Assessment
```

### Pattern 3: Change Impact Traceability
```
Change Request
    ↓ (affects)
Requirements
    ↓ (impacts)
Design Elements
    ↓ (requires)
Code Changes
    ↓ (necessitates)
Test Updates
    ↓ (produces)
Verification Evidence
```

## Implementation Considerations

### Audit Trail Requirements
```python
class AuditEntry:
    timestamp: datetime
    user: str
    action: str  # create, update, delete, approve
    entity_type: str
    entity_id: str
    old_value: Optional[dict]
    new_value: dict
    reason: str
    signature: Optional[str]  # Electronic signature
```

### Compliance Reporting
- **Traceability Matrix**: Requirements → Tests
- **Coverage Report**: Test coverage by requirement
- **Gap Analysis**: Untested/unimplemented requirements
- **Change Impact Report**: Affected artifacts by change
- **Verification Report**: Verification status by requirement

### Tool Qualification
For safety-critical systems, the RTM tool itself may require qualification:
- **Tool Confidence Level (TCL)**: Based on impact of tool failure
- **Qualification Data**: Test evidence, known issues
- **Configuration Management**: Version control, change history
- **User Documentation**: Complete, validated

## RTM System Features for Compliance

### Must-Have Features
1. **Bidirectional traceability**: Forward and backward links
2. **Immutable audit trail**: All changes logged
3. **Electronic signatures**: For approvals
4. **Version control**: Complete history
5. **Access control**: Role-based permissions
6. **Change management**: Workflow with approvals
7. **Reporting**: Compliance reports
8. **Export**: Standard formats (CSV, PDF, XML)

### Nice-to-Have Features
1. **Risk management integration**: ISO 14971, FMEA
2. **Test management integration**: Test execution tracking
3. **Document management**: Specification documents
4. **Workflow automation**: Approval routing
5. **Notification system**: Change alerts
6. **Dashboard**: Compliance metrics

## Compliance Validation

### Validation Activities
1. **Requirements validation**: Completeness, correctness
2. **Traceability validation**: All links verified
3. **Coverage validation**: 100% requirement coverage
4. **Tool validation**: IQ/OQ/PQ for RTM system
5. **Process validation**: Compliance with procedures

### Validation Evidence
- Traceability matrix (verified)
- Coverage reports (100%)
- Gap analysis (no gaps)
- Audit trail review (complete)
- Tool qualification report

