In recent years the Internet has become a source of data and information of indisputable importance and has immensely gained in acceptance and popularity. The World Wide Web (WWW or Web, for short), frequently named "the nervous system of the infor- tion society," offers numerous valuable services leaving no doubt about the signi?cance of the Web in our daily activities at work and at home. Consequently, we have a clear aspiration to meet the obvious need for effective use of its potential by making - provements in both the methods and the technology applied. Among the new research directions...