quality-attributes-taxonomy

# Quality Attributes Taxonomy

This skill provides a comprehensive framework for understanding and applying quality attributes (non-functional requirements) in system design.

## When to Use This Skill

**Keywords:** NFR, non-functional requirements, quality attributes, -ilities, scalability, reliability, availability, performance, security, maintainability, ISO 25010

**Use this skill when:**

- Defining non-functional requirements for a system
- Evaluating architectural trade-offs
- Conducting architecture reviews
- Preparing for system design interviews
- Ensuring all quality dimensions are considered
- Translating business needs to technical requirements

## What Are Quality Attributes?

Quality attributes (QAs) describe HOW a system performs, not WHAT it does. They're often called:

- Non-Functional Requirements (NFRs)
- The "-ilities" (scalability, reliability, etc.)
- Cross-cutting concerns
- System qualities

**Key insight:** Functional requirements define features; quality attributes define how well those features work.

## The Core Quality Attributes

### Primary Attributes (The Big 6)

| Attribute | Definition | Key Question |
| --------- | ---------- | ------------ |
| **Scalability** | Handle growing load | Can we grow 10x? 100x? |
| **Reliability** | Consistent correct operation | Does it work correctly every time? |
| **Availability** | System uptime | Is it running when needed? |
| **Performance** | Speed and throughput | How fast is it? |
| **Security** | Protection from threats | Is it safe from attacks? |
| **Maintainability** | Ease of change | Can we update it easily? |

### Secondary Attributes

| Attribute | Definition | Key Question |
| --------- | ---------- | ------------ |
| **Testability** | Ease of verification | Can we test it effectively? |
| **Observability** | System visibility | Can we see what's happening? |
| **Operability** | Ease of operation | Can we run it in production? |
| **Portability** | Platform independence | Can we mov