External characteristics are characteristics that a user of the software product is aware of, including the following:
- Correctness: The degree to which a system is free from faults in its specification, design, and implementation.
- Usability: The ease with which users can learn and use a system.
- Efficiency: Minimal use of system resources, including memory and execution time.
- Reliability: The ability of a system to perform its required functions under stated conditions whenever required—having a long mean time between failures.
- Integrity: The degree to which a system prevents unauthorized or improper access to its programs and its data. The idea of integrity includes restricting unauthorized user accesses as well as ensuring that data is accessed properly—that is, that tables with parallel data are modified in parallel, that date fields contain only valid dates, and so on.
- Adaptability: The extent to which a system can be used, without modification, in applications or environments other than those for which it was specifically designed.
- Accuracy: The degree to which a system, as built, is free from error, especially with respect to quantitative outputs. Accuracy differs from correctness; it is a determination of how well a system does the job it’s built for rather than whether it was built correctly.
- Robustness: The degree to which a system continues to function in the presence of invalid inputs or stressful environmental conditions.