Complex web applications and, more in general, digital artifacts, whose goals are to communicate information and services to a large number of users, have to pay special attention to their usability, or rather quality.
The quality of web sites (or more in general interactive applications) can be improved by taking into account the activity of usability, in which the quality for the end- users is defined and established.
Clearly, this is an arduous task for the designers (and in general for all the stakeholders involved in the development of the application).
Indeed, web applications are of growing complexity, address several targets, deal with complex content, have different communication goals. For all these reasons, they need to be well "usable" and efficient.
Evaluating the usability of a web application means trying to answer some crucial questions: e.g., How can we avoid users “getting lost” in the site? How is it possible to improve a navigation’s effectiveness? What kind of contents shouldn’t be missing? How is it possible to know whether the users have learnt anything from the site?
Lack of usability means issues in business generation.