Memento Project
Memento is a United States National Digital Information Infrastructure and Preservation Program (NDIIPP)-funded project aimed at making Web-archived content more readily discoverable.
The project is being led by the Los Alamos National Laboratory and Old Dominion University.
Rather than expecting people to know about the growing number of Web archives, and to guess which archive might hold an older version of the resource they’re looking for, Memento proposes to make archived content discoverable via the original URL that the searcher already knew about. Essentially, Memento is an attempt to permit users to view any web page as it looked on a given date in the past.
A variety of web archives exist, collecting specific revisions of web pages as they existed at a particular point in time. Memento allows a user to seamlessly transition between these archives in search of the best archived page matching the datetime for the page that they desire.
Memento is defined in RFC 7089 as an implementation of the time dimension of content negotiation, as defined by Tim Berners Lee in 1996. HTTP accomplishes negotiation of content via headers. The table below shows the different headers available for HTTP that allow clients and servers to find the content that the user desires.
text/plain image/png
en-US cz
gzip deflate
unicode-1-1
GMT
Memento provides the Accept-Datetime request header so that clients can provide a date to the server, and the server can provide the best archived version of a page for that date. This is referred to as datetime negotiation.
To understand Memento fully, one must realize that the Last-Modified header provided by HTTP does not necessarily reflect when a particular version of a web page came into existence. Also, the Last-Modified header may not exist in some cases. To provide more information, the Memento-Datetime header has been introduced to indicate when a specific representation of a web page was observed on the web.
...
Wikipedia