A lighthouse page is a page that the system thinks the user finds interesting. The system uses the lighthouses---separately---to evaluate each page fetched. A page is fetched if the system has some reason to believe that it might be related to one of the lighthouses. When pages are fetched they are each compared against every lighthouse. The system analyzes the differences and similarities between the new page and each lighthouse and keeps those pages that are strongly related to any one lighthouse, or are weakly related to several lighthouses. All other pages are put in a trash cluster (but not discarded).
Each lighthouse thus defines a cluster of pages that are in some way related to that lighthouse. When a simpleton downgrades a page and it is later highly rated by the user, or when a simpleton rates a page highly but the user subsequently never looks at, that simpleton is punished (which just means that either its decision algorithms are modified or there are several decision algorithms and the chance that those particular ones will be used in future for this particular lighthouse is reduced).
The system chooses lighthouses to be those pages that its user has looked at recently, or looked at intensely some time ago, or that are strongly related to more than one focus of attention (that is, other lighthouses). The lighthouses themselves become focuses of attention and they serve to direct the system's future behavior.
This means that initially the user model need only be the list of lighthouses. The pollsters detect lighthouses. The clusterers link pages to one or more lighthouses. The filters compare new pages against particular lighthouses. The collectors search for more pages like the lighthouses. The interface displays the lighthouses, and the pages nearest them (in whatever sense of the word "nearest" that the interface thinks is most relevant to the user at the moment.)
Consequently, a particular user's system can't be described solely in terms of its architecture. It is that architecture plus the lighthouses that the user has shown most interest in (however defined). The lighthouses become the memory around which everything revolves.