Runtime attributes (observable at runtime)
Usability: the level of human satisfaction from using the system. Usability includes matters of completeness, correctness, compatibility, as well as a friendly user interface, complete documentation, and technical support.
Reliability: the failure frequency, the accuracy of output results, the Mean-Time-to-Failure (MTTF), the ability to recover from failure, and the failure predictability.
Maintainability (extensibility, adaptability, serviceability, testability, compatibility, and configurability): the ease of software system change.