With the rapid growth of the Internet and the increasing popularity of the World Wide Web, web-based learning systems have become more and more popular. However, in general Web-based learning systems, learners may often get lost in the enormous educational materials (Eirinaki & Vazirgiannis, 2003; Murray, 2002). This kind of situation refers to a disorientation problem. In addition to the disorientation problem, general Web-based learning systems provide every learner with uniform course content and presentation without considering the different knowledge level of learners. Therefore, the course content may be insufficient or unnecessary for learners with different knowledge level. This kind of situation was referred to as cognitive-overhead problem by Murray (2002).