Web sites usability requirements specification & evaluation

World Wide Web has gained its dominant status in the information and services delivery world in recent years, but how to build a good usability web site is still a problem. In this paper, we proposed a methodology for structured use-centered quantitative full-life-cycle usability requirements specification and usability evaluation of web sites. Our approach is that: the system's usability is defined in terms of its consisting goal-tasks' usability; a goal-task's usability is defined in terms of several major usability aspects; each major usability aspect is further defined in terms of several basic use features. In this way, a quantitative web sites usability engineering framework is set up. According to this framework, each goal-task's usability requirements are specified in terms of its basic use features, and then are tested against to see if they are satisfied; a system's usability can be easily derived by combining its consisting goal-tasks' usabilities through a weighted scheme. This quantitative usability methodology is independent of, and therefore can be seamlessly integrated into, any engineering methodologies, processes and techniques.