During the last years web search engines have moved from the simple but inefficient syntactical analysis (first generation) to the more robust and usable web graph analysis (second generation). Much of the current research is focussed on the so-called third generation search engines that, in principle, inject human characteristics on how results are obtained and presented to the end user. Approaches exploited towards this direction include (among others): an alteration of PageRank  that takes into account user specific characteristics and bias the page ordering using the user preferences (an approach, though, that does not scale well with the number of users). The approach is further exploited in , where several PageRanks are computed for a given number of distinct search topics. A similar idea is used in , where the PageRank computation takes into account the content of the pages and the query terms the surfer is looking for. In , a decomposition of PageRank to basic components is suggested that may be able to scale the different PageRank computations to a bigger number of topics or even distinct users. Another approach to web search is presented in , where a rich extension of the web, called semantic web, and the application of searching over this new setting is described.