Memento: Time Travel for the Web

The Web is ephemeral. Many resources have representations that change overtime, and many of those representations are lost forever. A lucky few manage toreappear as archived resources that carry their own URIs. For example, somecontent management systems maintain version pages that reflect a frozen priorstate of their changing resources. Archives recurrently crawl the web to obtainthe actual representation of resources, and subsequently make those availablevia special-purpose archived resources. In both cases, the archival copies haveURIs that are protocol-wise disconnected from the URI of the resource of whichthey represent a prior state. Indeed, the lack of temporal capabilities in themost common Web protocol, HTTP, prevents getting to an archived resource on thebasis of the URI of its original. This turns accessing archived resources intoa significant discovery challenge for both human and software agents, whichtypically involves following a multitude of links from the original to thearchival resource, or of searching archives for the original URI. This paperproposes the protocol-based Memento solution to address this problem, anddescribes a proof-of-concept experiment that includes major servers of archivalcontent, including Wikipedia and the Internet Archive. The Memento solution isbased on existing HTTP capabilities applied in a novel way to add the temporaldimension. The result is a framework in which archived resources can seamlesslybe reached via the URI of their original: protocol-based time travel for theWeb.