A Pocket Guide to Web History

Web archives like the Internet Archive preserve the evolutionary history of large portions of the Web. Access to them, however, is still via rather limited interfaces – a search functionality is often missing or ignores the time axis. Time-travel search alleviates this shortcoming by enriching keyword queries with a time-context of interest. In order to be effective, time-travel queries require historical PageRank scores. In this paper, we address this requirement and propose rank synopses as a novel structure to compactly represent and reconstruct historical PageRank scores. Rank synopses can reconstruct the PageRank score of a web page as of any point during its lifetime, even in the absence of a snapshot of the Web as of that time. We further devise a normalization scheme for PageRank scores to make them comparable across different graphs. Through a comprehensive evaluation over different datasets, we demonstrate the accuracy and space-economy of the proposed methods.