---
title: "Requirements Engineering Guide"
description: "Comprehensive framework for gathering, analyzing, and managing software requirements"
categories: ["Guidelines"]
provide_notes: true
filters:
  - diagram
---

## Introduction to Requirements Engineering

Requirements Engineering is a systematic approach to eliciting, documenting, validating, and managing requirements throughout the software development lifecycle. This guide provides a structured framework for modern requirements practices, methodologies, and techniques that lead to successful software development outcomes.

## Requirements Engineering Process Overview

The requirements engineering process consists of iterative activities that transform stakeholder needs into well-defined requirements:

```{mermaid}
graph TD
    A[Elicitation] --> B[Analysis]
    B --> C[Specification]
    C --> D[Validation]
    D --> E[Management]
    E --> A
    
    style A fill:#f9d5e5,stroke:#333
    style B fill:#eeeeee,stroke:#333
    style C fill:#d4f1f9,stroke:#333
    style D fill:#d8f3dc,stroke:#333
    style E fill:#ffcccb,stroke:#333
```

## Types of Requirements

### Functional Requirements

Functional requirements define specific behaviors, capabilities, and functions that a system must perform to meet user needs.

- Describe what the system should do
- Detail the features and services provided
- Specify behaviors under particular conditions
- Define interactions between users and the system
- Often expressed as "The system shall..."

### Example: Functional Requirement Specification

**FR-103**: User Authentication

**Description**: The system must authenticate users before granting access to protected resources.

**Details**:
- The system shall provide a login interface requiring username and password
- The system shall validate credentials against the user database
- The system shall enforce password complexity requirements
- The system shall lock accounts after 5 failed login attempts
- The system shall provide a password recovery mechanism

**Priority**: Must have  
**Source**: Security policy SP-42  
**Dependent requirements**: FR-101, FR-102  
**Verification method**: Security testing

### Non-Functional Requirements

Non-functional requirements define quality attributes, constraints, and characteristics that affect how the system performs its functions.

- Performance: Response times, throughput, resource utilization
- Security: Authentication, authorization, data protection
- Usability: User interface, accessibility, learning curve
- Reliability: Fault tolerance, recoverability, availability
- Compatibility: Platform support, integration capabilities
- Scalability: Growth capacity, load handling
- Maintainability: Ease of updates, modularity, documentation

## User Stories

User stories are short, simple descriptions of functionality from an end user perspective. They follow this format:

**As a [user type], I want [goal] so that [benefit/value].**

Example:
> As a mobile app user, I want to save my data locally so that I can access it offline.

### User Story Quality Criteria: The INVEST Model

Each user story should meet the INVEST criteria:

- **I**ndependent: Can be developed and delivered separately
- **N**egotiable: Details can be discussed and refined
- **V**aluable: Delivers specific value to users or stakeholders
- **E**stimable: Team can reasonably estimate development effort
- **S**mall: Fits within a single iteration
- **T**estable: Has clear acceptance criteria

#### Acceptance Criteria
Acceptance criteria define when a user story is complete. They should be:

- Written in clear, unambiguous language
- Testable with specific conditions
- Include both happy path and edge cases
- Defined before development begins

Example:
> **Given** I am a logged-in user  
> **When** I navigate to my profile  
> **And** I click the "Edit Profile" button  
> **And** I update my profile information  
> **And** I click "Save"  
> **Then** my updated information should be displayed  
> **And** I should see a success message

## Requirements Documentation Methods

### Scenarios and Acceptance Tests

Scenarios describe specific examples of system behavior using the Given-When-Then format:

```gherkin
@test-type @priority @scope
Scenario: E[XX]-F[XX]-S[XX] - [Descriptive Title]
  Given [initial context]
  When [action occurs]
  Then [expected outcome]
```

#### Example Scenarios:

```gherkin
@happy-path @smoke @automated
Scenario: E01-F01-S01 - Successful User Registration
  Given a new user on the registration page
  When they complete the registration form with valid data
  Then their account should be created
  And they should receive a confirmation email

@edge-case @security
Scenario: E01-F01-S02 - Registration with Existing Email
  Given a new user on the registration page
  And an existing account with email "test@example.com"
  When they attempt to register with the same email
  Then registration should be prevented
  And they should see an error message
```

For detailed scenario templates and examples, see the [Scenarios and Acceptance Tests Template](../templates/requirements/scenarios.qmd).

### Gherkin Specifications and Numbering System

Gherkin specifications should follow a hierarchical numbering format for clear organization:

- EPIC: E[01-99] (e.g., E01)
- Feature: E[01-99]-F[01-99] (e.g., E01-F01)
- User Story: E[01-99]-F[01-99]-US[01-99] (e.g., E01-F01-US01)
- Scenario: E[01-99]-F[01-99]-S[01-99] (e.g., E01-F01-S01)
- Acceptance Test: E[01-99]-F[01-99]-TA[01-99] (e.g., E01-F01-TA01)

Example Structure:
```gherkin
## EPIC: E01 - [User Account Management]

### Feature: E01-F01 - [User Registration]

@functional @critical @sprint-1 @user-role-all
**User Story:** E01-F01-US01 - As a new user, I want to create an account so that I can access the application's features.

@happy-path @smoke @automated
Scenario: E01-F01-S01 - Successful Registration
  Given the user is on the registration page
  When the user enters valid registration information
  And submits the registration form
  Then a new account should be created
  And the user should be redirected to the welcome page
```

### Use Cases

Use cases describe interactions between actors and the system to achieve specific goals, typically including:

- Actors involved
- Preconditions
- Main success scenario
- Alternative paths
- Postconditions

### Data Requirements

Data requirements define the structure, relationships, and characteristics of data in the system:

1. **Data Structures**
   - Entity definitions
   - Attributes and data types
   - Relationships and cardinality
   - Data constraints and validation rules

2. **Data Quality Requirements**
   - Accuracy standards
   - Completeness requirements
   - Consistency rules
   - Timeliness requirements

3. **Data Lifecycle**
   - Creation and acquisition
   - Storage and retention
   - Archival and backup
   - Deletion and purging

Example Data Requirement:
```yaml
Entity: Customer
Description: Represents a registered user of the system
Attributes:
  - id: UUID (primary key)
  - email: String (unique, validated)
  - name: String (required)
  - created_at: Timestamp
Relationships:
  - has_many: Orders
  - has_one: ShippingAddress
Constraints:
  - email must be unique
  - password must meet security policy
Quality:
  - 99.99% data accuracy
  - < 1s retrieval time
```

For detailed templates and examples, see the [Data Requirements Template](../templates/requirements/data-requirements-template.qmd).

### External Interface Requirements

External interface requirements define how the system interacts with other systems, users, hardware, and software:

1. **User Interfaces**
   - Visual elements and layouts
   - Navigation patterns
   - Input/output methods
   - Accessibility standards

2. **System Interfaces**
   - API specifications
   - Data formats
   - Communication protocols
   - Integration points

Example Interface Requirement:
```yaml
Interface: Payment Gateway API
Type: REST API
Description: Integration with payment processing service
Specifications:
  - Protocol: HTTPS
  - Authentication: OAuth 2.0
  - Data Format: JSON
  - Endpoints:
    - POST /api/v1/payments
    - GET /api/v1/transactions
Requirements:
  - Max response time: 3 seconds
  - 99.99% availability
  - End-to-end encryption
```

For detailed templates and examples, see the [External Interface Requirements Template](../templates/requirements/external-interface-requirements.qmd).

### Requirements Specification Documents

Formal documents that detail:

- System overview: Provides a high-level description of the system, its purpose, scope, and objectives
- Functional and non-functional requirements: Details specific behaviors (functional) and quality attributes (non-functional) of the system
- Data requirements: Specifies data structures, relationships, and persistence needs
- External interface requirements: Documents how the system interacts with external components, including APIs, UIs, and hardware interfaces
- Constraints and assumptions: Lists technical, business, and environmental limitations and presumptions that impact the system
- Traceability matrix: Maps relationships between requirements, design components, and test cases to ensure complete coverage

### System Overview

The system overview provides a high-level understanding of the system's purpose, scope, and key components:

1. **System Purpose and Scope**
   - Primary goals and objectives
   - Target users and stakeholders
   - Key value propositions
   - Business objectives

2. **System Context**
   ```mermaid
   graph TD
       A[System] --> B[External System 1]
       A --> C[External System 2]
       A --> D[External System 3]
       E[User Type 1] --> A
       F[User Type 2] --> A
   ```

3. **Technology Stack**
   | Layer | Technologies | Rationale |
   |-------|-------------|-----------|
   | Frontend | [Technologies] | [Justification] |
   | Backend | [Technologies] | [Justification] |
   | Database | [Technologies] | [Justification] |
   | Infrastructure | [Technologies] | [Justification] |

For detailed templates and examples, see the [System Overview Template](../templates/requirements/system-overview-template.qmd).

## Requirements Gathering Process

An effective requirements gathering process typically includes:

1. **Stakeholder Identification**: Determine who has input on or is affected by the system.

2. **Elicitation Techniques**:
   - Interviews with stakeholders
   - Workshops and focus groups
   - Surveys and questionnaires
   - Observation of current processes
   - Analysis of existing documentation
   - Prototyping and user feedback

3. **Analysis and Refinement**:
   - Remove ambiguities and resolve conflicts
   - Identify gaps and inconsistencies
   - Elaborate high-level requirements into detailed specifications
   - Validate requirements with stakeholders

4. **Documentation**:
   - Create formal requirements documentation using appropriate templates
   - Establish traceability between requirements
   - Manage requirements versioning

5. **Prioritization**:
   - Apply the MoSCoW method (Must have, Should have, Could have, Won't have)
   - Consider business value, risk, dependencies, effort, and time constraints
   - Create a prioritized backlog for implementation

6. **Validation and Verification**:
   - Review requirements with stakeholders
   - Ensure requirements are testable
   - Check for completeness and consistency
   - Validate alignment with business goals

## Requirements Visualization Techniques

Visual representations often communicate requirements more effectively than text alone:

### User Journey Maps
Visualize the end-to-end user experience through a service or product, highlighting touchpoints, emotions, and pain points.

### Story Maps
Organize user stories into a narrative flow that shows the user journey horizontally and details vertically.

### Impact Mapping
Connect business goals to user needs, deliverables, and development activities in a hierarchical diagram.

### Event Storming
Collaborative modeling technique using sticky notes to explore domain events, commands, aggregates, and policies.

### Example Story Map

```{mermaid}
graph TD
    subgraph "User Journey"
        A["Sign Up"] --> B["Create Profile"]
        B --> C["Connect Devices"]
        C --> D["Track Activity"]
        D --> E["View Reports"]
    end
    
    subgraph "Epic: Sign Up"
        A1["Email Sign Up"]
        A2["Social Sign Up"]
        A3["Account Verification"]
    end
    
    subgraph "Epic: Create Profile"
        B1["Basic Info"]
        B2["Fitness Goals"]
        B3["Health Metrics"]
    end
    
    A --- A1
    A --- A2
    A --- A3
    B --- B1
    B --- B2
    B --- B3
```

## Domain-Driven Design in Requirements Engineering

Domain-Driven Design (DDD) provides a powerful approach to requirements engineering by focusing on the core domain and domain logic.

### Ubiquitous Language

- Create a shared language between developers and domain experts
- Document domain terminology in a glossary
- Use consistent terminology in requirements, code, and tests

### Bounded Contexts

- Identify different contexts within the system where terms might have different meanings
- Document context boundaries and relationships
- Align requirements organization with bounded contexts

### Example Domain Model

```{.plantuml}

### Example Domain Model

```{.plantuml}
@startuml
' Set horizontal layout
left to right direction
skinparam nodesep 80
skinparam ranksep 60

class Order {
    +OrderId
    +OrderDate
    +Status
    +calculateTotal()
}

class Customer {
    +CustomerId
    +Name
    +Address
    +placeOrder()
}

class OrderItem {
    +ProductId
    +Quantity
    +UnitPrice
    +calculateSubtotal()
}

class Product {
    +ProductId
    +Name
    +Description
    +Price
}

Customer "1" --> "*" Order : places
Order "1" *-- "*" OrderItem : contains
OrderItem "*" --> "1" Product : references

@enduml
```

## Requirements Traceability

### Traceability Framework

A comprehensive traceability framework should include:

| Requirement ID | Source | User Story | Design Document | Implementation | Test Case | Status |
|---------------|--------|------------|-----------------|----------------|-----------|--------|
| E01-F01-S01 | Client Meeting #2 | E01-F01-US01 | DB Schema v1.2 | UserController.kt | E01-F01-TA01 | Verified |

### Traceability Tags

Use these special tags to establish traceability links:

- `@source`: Links to requirement source (e.g., `@source:PRD-v1.2`)
- `@implements`: Links to design document (e.g., `@implements:design-doc-login`)
- `@code`: Links to implementation (e.g., `@code:com.example.UserController`)
- `@tests`: Links to test implementation (e.g., `@tests:UserRegistrationTest`)

### Requirement Dependencies and Relationships

Document relationships between requirements using these conventions:

| Relationship | Syntax | Description |
|-------------|--------|-------------|
| Depends on | `@depends-on:E01-F02` | Requirement depends on another being implemented first |
| Extends | `@extends:E01-F02` | Requirement extends functionality of another |
| Conflicts with | `@conflicts-with:E01-F02` | Potential conflict needing resolution |
| Replaces | `@replaces:E01-F02` | Requirement supersedes an earlier one |
| Related to | `@related-to:E01-F02` | General relationship with another requirement |

### Traceability Matrix Overview

A comprehensive traceability matrix maps relationships between:

1. **Business Requirements to System Requirements**
   - Links high-level business needs to specific system features
   - Ensures complete coverage of business objectives
   - Identifies gaps in implementation

2. **Requirements to Design Components**
   - Maps requirements to architectural components
   - Validates technical implementation approach
   - Tracks design coverage

3. **Requirements to Test Cases**
   - Links requirements to verification methods
   - Ensures complete test coverage
   - Validates requirement testability

Example Matrix:

| Requirement ID | Business Req | User Story | Design Doc | Test Case | Status |
|---------------|--------------|------------|------------|-----------|--------|
| FR-103 | BR-001 | US-001 | DESIGN-001 | TC-001 | Verified |
| NFR-201 | BR-002 | US-002 | DESIGN-002 | TC-002 | In Progress |

For detailed templates and examples, see the [Traceability Matrix Template](../templates/requirements/traceability-matrix-template.qmd).

## Using Requirement Tags

Tags serve multiple purposes in requirements management:

### Priority Tags
- `@critical` - Must be implemented for core functionality
- `@high` - Important feature needed soon
- `@medium` - Standard priority feature
- `@low` - Nice-to-have feature

### Type Tags
- `@functional` - Core behavior functionality
- `@non-functional` - Quality attributes
- `@ui` - User interface related
- `@api` - API functionality
- `@data` - Data handling
- `@integration` - External system integration

### Testing Tags
- `@smoke` - Basic functionality verification
- `@regression` - Regression detection
- `@automated` - Automated test scenarios
- `@manual` - Manual test scenarios
- `@performance` - Performance testing
- `@security` - Security testing
- `@accessibility` - Accessibility testing
- `@usability` - Usability testing

### Status Tags
- `@wip` - Work in progress
- `@blocked` - Implementation blocked
- `@implemented` - Feature implemented
- `@verified` - Feature tested and verified

## Best Practices for Requirements Engineering

- **Involve the right stakeholders**: Ensure all relevant perspectives are considered.
  
- **Use clear, unambiguous language**: Avoid vague terms like "user-friendly," "fast," or "efficient" without measurable criteria.
  
- **Be specific and measurable**: Define quantifiable criteria for non-functional requirements.
  
- **Maintain traceability**: Link requirements to business goals, design elements, code implementation, and test cases.
  
- **Iteratively refine requirements**: Requirements evolve; plan for ongoing refinement.
  
- **Document assumptions and constraints**: Make implicit limitations explicit.
  
- **Use visual aids**: Diagrams, mockups, and prototypes can clarify complex requirements.
  
- **Establish a glossary**: Define domain-specific terms to ensure shared understanding.
  
- **Consider edge cases and exceptions**: Document how the system should handle unusual situations.
  
- **Validate with acceptance criteria**: Each requirement should have clear criteria for determining when it's met.

## Modern Requirements Practices

### Requirements in DevOps Environments

Modern DevOps practices change how requirements are managed:

#### Continuous Requirements

- Requirements evolve alongside continuous delivery
- Feedback loops inform requirement adjustments
- Feature flags enable progressive delivery of requirements
- A/B testing validates requirement assumptions

#### Requirements as Code

- Version control requirements alongside code
- Automated validation of requirements
- Requirements expressed as executable specifications
- Infrastructure requirements defined as code

#### Integration into CI/CD Pipeline

- Automated requirements validation
- Requirements compliance verification
- Traceability enforcement
- Release notes generation from requirements changes

### Agile Adaptation

#### Progressive Refinement

Progressive refinement is a core agile practice that involves:

- Starting with high-level epics and gradually breaking them down
- Regular refinement sessions with stakeholders
- Continuous evolution of requirements based on feedback
- Using story splitting techniques for complex requirements
- Maintaining a healthy backlog refinement cadence

#### Living Documentation

Living documentation keeps requirements aligned with the evolving system:

- Automated testing as documentation (Behavior-Driven Development)
- Wiki-based requirements that evolve with the product
- Version-controlled requirements alongside code
- Automated generation of documentation from code and tests
- Regular review and updates based on implementation feedback

#### Just-enough Documentation

- Balance between documentation and agility
- Focus on essential information capture
- Documentation that serves a clear purpose

### AI-Assisted Requirements

- Natural language processing for requirement analysis
- Automated consistency checking
- Smart requirement classification

## Requirements Management Tools

Various tools can help with requirements gathering and management:

- Specialized requirements management tools (e.g., Jira, Azure DevOps, ReqSuite)
- Documentation tools with requirements templates (e.g., Confluence, SharePoint)
- Modeling tools for visual requirements (e.g., Lucidchart, Draw.io)
- Collaborative workspaces (e.g., Miro, Mural) for requirements workshops
- Version control systems for requirements documentation

## Requirements Templates and Frameworks {#sec-templates}

For detailed templates and frameworks to document requirements effectively, see our standardized templates in the [Requirements Templates Guide](templates/index.qmd):

- [System Requirements Specification](templates/system-requirements-specification.qmd)
- [System Overview](templates/system-overview.qmd)
- [Requirements Glossary](templates/requirements-glossary.qmd)
- [Functional Requirements](templates/functional-requirements.qmd)
- [Non-functional Requirements](templates/non-functional-requirements.qmd)
- [User Stories](templates/user-stories.qmd)
- [Use Cases](templates/use-cases.qmd)
- [Data Requirements](templates/data-requirements.qmd)
- [Interface Requirements](templates/interface-requirements.qmd)
- [Constraints and Assumptions](templates/constraints-assumptions.qmd)
- [Requirements Traceability](templates/requirements-traceability.qmd)

## Project Constraints and Assumptions

Understanding and documenting constraints and assumptions is crucial for successful requirements engineering:

### Types of Constraints

1. **Business Constraints**
   - Regulatory requirements
   - Budget limitations
   - Timeline restrictions
   - Resource availability

2. **Technical Constraints**
   - Hardware limitations
   - Software dependencies
   - Integration requirements
   - Performance boundaries

3. **Environmental Constraints**
   - User environment
   - System environment
   - Infrastructure requirements
   - Deployment restrictions

### Managing Assumptions

1. **Documentation**
   - Clearly state each assumption
   - Provide rationale
   - Identify risks
   - Plan validation approach

2. **Validation Process**
   - Regular review of assumptions
   - Update as new information emerges
   - Track impact on requirements
   - Maintain traceability

For detailed templates and guidance on documenting constraints and assumptions, see the [Constraints and Assumptions Template](../templates/requirements/constraints-and-assumptions-template.qmd).

## Common Challenges in Requirements Engineering

- **Scope creep**: Continuously expanding requirements
- **Unstated assumptions**: Implicit requirements that aren't documented
- **Conflicting requirements**: Contradictory needs from different stakeholders
- **Analysis paralysis**: Excessive detail slowing down the process
- **Ambiguity**: Unclear or vague specifications
- **Over-specification**: Dictating implementation rather than requirements
- **Changing requirements**: Managing evolving needs during development

Addressing these challenges requires strong communication, stakeholder engagement, appropriate methodology selection, and effective requirements management tools and processes.

## Requirements Validation Techniques

Requirements validation ensures that the documented requirements accurately represent stakeholder needs and can be implemented into a working system that meets those needs.

### Review Techniques

#### Peer Reviews
- **Description**: Systematic examination of requirements by peers and colleagues
- **Benefits**: Identifies inconsistencies and ambiguities early
- **Process**: 
  1. Distribute requirements to reviewers
  2. Allow time for individual review
  3. Collect and consolidate feedback
  4. Address issues identified

#### Walkthrough Sessions
- **Description**: Presenter guides stakeholders through requirements step by step
- **Benefits**: Creates shared understanding and surfaces questions
- **Process**:
  1. Present requirements in logical order
  2. Encourage questions and discussion
  3. Document concerns and suggested improvements
  4. Follow up with revisions

#### Formal Inspections
- **Description**: Structured review process with defined roles and procedures
- **Benefits**: High defect detection rate, provides metrics on requirements quality
- **Roles**:
  - Moderator: Manages the process
  - Reader: Presents the material
  - Recorder: Documents issues
  - Inspector: Reviews for specific issues
- **Process**:
  1. Planning and preparation
  2. Inspection meeting
  3. Rework
  4. Follow-up verification

#### Stakeholder Reviews
- **Description**: Validation sessions with business stakeholders
- **Benefits**: Ensures requirements meet business needs, builds buy-in
- **Best Practices**:
  - Prepare executive summaries for high-level stakeholders
  - Use visual aids to help explain technical concepts
  - Document sign-off and approval

### Validation Methods

#### Prototyping
- **Types**:
  - Low-fidelity: Paper sketches, wireframes
  - Medium-fidelity: Interactive mockups
  - High-fidelity: Working prototypes
- **Benefits**:
  - Makes abstract requirements tangible
  - Allows early user feedback
  - Reveals unstated requirements
- **Example Process**:
  1. Create prototype based on requirements
  2. Conduct user testing sessions
  3. Collect feedback
  4. Refine requirements based on insights

#### Requirements Testing
- **Description**: Creating test cases directly from requirements
- **Techniques**:
  - Requirements-based test design
  - Boundary value analysis
  - Equivalence partitioning
- **Example**:
  ```
  Requirement: The system shall accept passwords between 8-20 characters
  
  Test Cases:
  - 7 characters (invalid)
  - 8 characters (valid)
  - 20 characters (valid)
  - 21 characters (invalid)
  ```

#### Model Validation
- **Description**: Validating requirements through models and simulations
- **Modeling Techniques**:
  - UML diagrams
  - Business process models
  - State machines
  - Data models
- **Validation Approach**:
  1. Create models representing requirements
  2. Walk through scenarios using models
  3. Verify logic and completeness
  4. Update requirements based on model insights

#### Use Case Simulation
- **Description**: Mentally executing use cases step by step
- **Benefits**:
  - Validates flow and logic
  - Identifies missing steps and conditions
  - Tests alternative paths
- **Process**:
  1. Select a use case
  2. Define test scenarios
  3. Execute each step mentally or with simple tools
  4. Document issues and gaps found

### Validation Checklist

A comprehensive requirements validation should verify the following qualities:

#### Completeness
- All required functionality is specified
- All interfaces are defined
- All constraints are documented
- No "TBD" (To Be Determined) items remain without explanation

#### Consistency
- No contradictions between requirements
- Consistent terminology throughout
- Consistent level of detail
- Alignment with higher-level requirements

#### Feasibility
- Technical feasibility assessment
- Schedule feasibility evaluation
- Budget feasibility check
- Operational feasibility confirmation

#### Testability
- Each requirement can be verified objectively
- Clear acceptance criteria exist
- Quantifiable metrics where appropriate
- Test cases can be derived

#### Traceability
- Each requirement is uniquely identified
- Links to source (business need, stakeholder, etc.)
- Forward traceability to design and tests
- Backward traceability to higher-level requirements

#### Unambiguity
- Clear, precise language
- Measurable criteria where applicable
- No subjective terms without definition
- Single interpretation possible

#### Correctness
- Reflects stakeholder needs accurately
- Aligns with business objectives
- Conforms to standards and regulations
- Technically sound

### Validation Documentation

Document the results of validation activities to ensure traceability and accountability:

1. **Validation Report**
   - Summary of validation activities
   - Issues identified
   - Resolution actions
   - Validation status of each requirement

2. **Review Record**
   - Date and participants
   - Requirements reviewed
   - Comments and issues raised
   - Decisions made

3. **Formal Sign-off**
   - Stakeholder acknowledgment
   - Approval signatures
   - Conditions of approval
   - Date of validation

## Requirements Artifacts Relationships

### Hierarchy and Relationships

```mermaid
graph TD
    E[Epic] --> F[Feature]
    F --> US[User Story]
    US --> FR[Functional Requirement]
    US --> NFR[Non-Functional Requirement]
    FR --> S[Scenario]
    NFR --> S
    US --> UC[Use Case]
    UC --> S
    S --> AT[Acceptance Test]
```

### Requirements Artifact Comparison

| Aspect | User Story | Use Case | Functional Req | Non-Functional Req | Scenario |
|--------|------------|----------|----------------|-------------------|-----------|
| Focus | User value | User interaction | System behavior | System qualities | Specific example |
| Format | As a/I want/So that | Steps & flows | System shall | System shall be | Given/When/Then |
| Scope | Single feature slice | Complete interaction | Specific function | Quality attribute | Single interaction path |
| Level | Business | User interaction | Technical | Technical | Implementation |
| Purpose | Planning | Design | Specification | Constraints | Validation |

### Relationships and Mappings

1. **Epic to Features**
   - Epic: Large initiative (e.g., "User Account Management")
   - Features: Major components (e.g., "Registration", "Authentication")

2. **Features to User Stories**
   ```gherkin
   Feature: E01-F01 - User Registration
   
   User Story: E01-F01-US01 - As a new user...
   User Story: E01-F01-US02 - As a registered user...
   ```

3. **User Stories to Requirements**
   ```gherkin
   User Story: E01-F01-US01
   @implements-fr:FR-103 // Authentication requirement
   @implements-nfr:NFR-201 // Response time requirement
   ```

4. **Requirements to Scenarios**
   ```gherkin
   FR-103: User Authentication
   
   Scenario: E01-F01-S01 - Successful Login
   Scenario: E01-F01-S02 - Failed Login
   ```

5. **Use Cases to Scenarios**
   ```gherkin
   Use Case: UC-01 - User Login Process
   
   Main Scenario: E01-F01-S01 - Successful Login
   Alternative: E01-F01-S02 - Failed Login
   Exception: E01-F01-S03 - Account Locked
   ```

### Key Differences

1. **User Stories vs Use Cases**
   - User Stories: Brief, focused on value
   - Use Cases: Detailed, focused on interaction steps

2. **Functional vs Non-Functional Requirements**
   - Functional: What the system does
   - Non-Functional: How well the system does it

3. **Scenarios vs Use Cases**
   - Scenarios: Specific instances/examples
   - Use Cases: Complete interaction flows

4. **Requirements vs Tests**
   - Requirements: Specify what's needed
   - Tests: Verify implementation meets requirements

### Example Flow

```gherkin
# Epic
E01 - User Account Management

# Feature
E01-F01 - User Registration

# User Story
E01-F01-US01 - As a new user, I want to create an account...

# Functional Requirement
FR-103 - The system shall authenticate users...

# Non-Functional Requirement
NFR-201 - Registration process shall complete within 2 seconds...

# Use Case
UC-01 - User Registration Process
1. User navigates to registration
2. System displays form
3. User submits information
...

# Scenario
E01-F01-S01 - Successful Registration
Given a new user on the registration page
When they submit valid information
Then their account is created

# Acceptance Test
E01-F01-TA01 - Verify Registration Success
Given test user data "test@example.com"
When registration form is submitted
Then database contains new user
And welcome email is sent
```

## Requirements Documentation Types {#sec-doc-types}

Requirements documentation follows a hierarchical structure:

1. **System Requirements Specification (SRS)**
   - Complete system documentation
   - High-level overview
   - All requirement types

2. **User Stories and Use Cases**
   - Business value focused
   - User interaction flows
   - Acceptance criteria

3. **Technical Requirements**
   - Functional specifications
   - Non-functional attributes
   - Interface definitions

4. **Supporting Documentation**
   - Data requirements
   - Constraints and assumptions
   - Traceability information

### Documentation Structure
```mermaid
graph TD
    SRS[System Requirements Specification] --> US[User Stories]
    SRS --> UC[Use Cases]
    SRS --> FR[Functional Requirements]
    SRS --> NFR[Non-Functional Requirements]
    SRS --> DR[Data Requirements]
    SRS --> IR[Interface Requirements]
    US --> AC[Acceptance Criteria]
    UC --> SC[Scenarios]
    FR --> TS[Test Specifications]
    NFR --> VM[Validation Methods]
```

### Document Dependencies

| Document Type | Depends On | Influences |
|--------------|------------|------------|
| SRS | Business Requirements | All other docs |
| User Stories | SRS | Functional Reqs |
| Use Cases | User Stories | Scenarios |
| Functional Reqs | User Stories | Test Specs |
| Non-Functional Reqs | SRS | Validation |

## Requirements Analysis Techniques

### Behavior-Driven Development (BDD)

**Principle**: Define expected system behaviors through scenarios understandable by all stakeholders.

**Implementation**:
- Use of Gherkin format (Given-When-Then)
- Example Mapping sessions to develop scenarios
- Automated tests directly linked to specifications

**Recommended Tools**:
- Cucumber, Specflow, JBehave
- FitNesse for acceptance testing

**References**:
- "BDD in Action" by John Ferguson Smart
- "Specification by Example" by Gojko Adzic

### Use Case Modeling

**Principle**: Document interactions between actors and the system to achieve specific goals.

**Recommended Structure**:
- Primary and secondary actors
- Pre and post conditions
- Main flow and alternatives
- Extensions and exceptions

**Documentation Format**:
```
Use Case: [Use Case Name]
Primary Actor: [Actor]
Preconditions: [Required Conditions]
Main Flow:
1. [Step 1]
2. [Step 2]
...
Alternative Flows:
- [Condition]: [Action Sequence]
Postconditions: [System State After Execution]
```

**References**:
- "Writing Effective Use Cases" by Alistair Cockburn
- "UML Distilled" by Martin Fowler

## Requirements Prioritization

### Prioritization Methods

**Recommended Techniques**:

1. **MoSCoW**:
   - Must have: Essential features
   - Should have: Important features
   - Could have: Desirable features
   - Won't have: Postponed features

2. **Weighted Scoring**:
   - Business value (30-50%)
   - Technical complexity (20-30%)
   - Risk (15-25%)
   - Cost (10-20%)

3. **User Story Mapping**:
   - Horizontal organization by user activities
   - Vertical organization by priority
   - Identification of coherent releases

**References**:
- "User Story Mapping" by Jeff Patton
- "Software Requirements" by Karl Wiegers and Joy Beatty

### Release Planning

**Recommended Structure**:
- MVP (Minimum Viable Product): Core features only
- Incremental releases: 4-6 weeks per release
- Priority reassessment after each user feedback