Notation

The Web is characterized by an extremely dy-namic nature, as it is proved by the rapid and significant growth it has experimented in the last decade and by its continuous evolution through creation or deletion of pages and hy-perlinks. Consequently, analyzing the temporal evolu-tion of the Web has become a crucial task that can provide search engines with valuable infor-mation for refining crawling policies, improv-ing ranking models or detecting spam. We study one year of data about the United Kingdom Web, collected by LAWa from June, 2006 to May, 2007. Twelve monthly snapshots of about 100M pages each were collected using UbiCrawler [1]. The web graphs of the single snapshots were created using WebGraphb. A first analysis of the data is presented in [2]. We study the hostgraph, i.e., the graph in which every node corresponds to a site, whereas a di-rected edge from one node to another repre-sents the existence of hyperlinks between pages belonging to two different hosts