Software Quality Part 3: Quality Attributes & Models

Study Notes

Quality attributes are measurable or observable characteristics of products and processes.
They are used early in the development process to identify user quality requirements.
Each system has specific and unique quality needs, which are a function of the purpose of the application.
Quality attributes can be classified into internal and external quality attributes:
- Internal: Derived immediately from the product or process description.
- External: Derived from the relationship between the environment and the system.

Internal quality concerns the developers/maintainers of the software, making it easy to change, add new features, and test.
External quality concerns the users of the software, measuring how the system meets the requirements of its stakeholders.
- Examples of internal quality attributes: Maintainability, Flexibility, Portability, Reusability, Readability, Testability, Understandability.
- Examples of external quality attributes: Correctness, Usability, Efficiency, Reliability, Integrity, Adaptability, Accuracy, Robustness.

Maintainability: Easy to change and adapt to new requirements, measured in terms of change logs and impact analysis.
Correctness: Lack of bugs and defects, measured in terms of defect rate.
Usability: Sufficiently convenient for the intended users, measured in terms of user satisfaction.
Reliability: Does not fail or crash often, measured in terms of failure rate.
Capability: Does all that is required, measured in terms of requirements coverage.
Performance: Fast and small enough, measured in terms of speed and space usage.
Installability: Convenient and fast to install, measured in terms of user satisfaction.
Documentation: Well-documented, measured in terms of user satisfaction.
Availability: Easy to access and available when needed, measured in terms of user satisfaction.

A quality model is a set of selected quality characteristics (attributes) and sub-characteristics together with the assigned measures.
The quality model provides the basis for specifying quality requirements and evaluating quality.
Well-known software quality models include: McCall Model, Boehm Model, FURPS Model, Dromey Model, and ISO/IEC 9126 Model.

Classifies 11 quality factors (attributes) into three categories: Product Revision, Product Transition, and Product Operations.
Product Revision factors:
- Maintainability
- Flexibility
- Testability
Product Transition factors:
- Portability
- Reusability
- Interoperability
Product Operations factors:
- Correctness
- Reliability
- Efficiency
- Integrity
- Usability