Over the past weeks, the
Memento team has worked with colleagues at
BibSonomy to enable Memento-related functionality for BibSonomy bookmarks.
The Memento "Time Travel for the Web" protocol specified in
RFC 7089 extends the
HTTP protocol with datetime negotiation, a variant of content negotiation. A Memento client
requests an old version of a resource by expressing the resource's original URI along with the datetime of the version it is interested in.
A Memento server, such as a web archive, responds with an archived snapshot of the resource that is temporally closest to the
datetime requested by the client. A Memento Aggregator simultaneously polls multiple web archives and returns the
temporally closest snapshot available irrespective of the archive it resides in.
Two features that use Memento infrastructure were added for BibSonomy Bookmarks:
- Bookmarked links are annotated with a
data-versiondate attribute that
conveys the datetime of bookmarking. This attribute, as well as the related data-versionurl, were first proposed in the Memento-related
Missing Link document that explores annotating links with temporal information as a means to
increase link robustness and to allow revisiting linked resources as they were seen by the creator of a link. Both attributes make use
of an extensibility mechanism
offered by HTML5 that allows the introduction of private data- attributes.
The Memento extension for Chrome supports both attributes. For bookmarked links in
BibSonomy, the extension presents a menu item Get at link date ..., which allows to look for archived snapshots of the bookmarked page
from around the time it was bookmarked. This feature is demonstrated in the below image. At the left hand side, a user clicks the link to the
website of the Raw visualization tool and receives the current version of the page in response.
At the right hand side, a user right-clicks the same link in a Chrome browser that has the Memento
extension installed. Since that link is annotated with the datetime of bookmarking -
expressed as the attribute data-versiondate="2014-03-16T17:42:12+01:00" on the link - the Memento extension uses the provided date for
web time travel and tries to find the archived snapshot of the Raw site closest to the date of bookmarking. It finds a snapshot dated March 7 2014 in the archive.today web archive that looks
rather different than the current version.
- The same functionality is available without the Memento extension for Chrome by
clicking the little clock at the bottom of the bookmarked item. Doing
so initiates a request by a Memento client at the end of BibSonomy
that is targeted at the Memento Aggregator and that results in a
redirect to a temporally appropriate Memento.
Both features are really neat and I would like to thank Robert Jäschke and his
colleagues at BibSonomy for making this happen and Martin Klein at the Memento
end for initiating the collaboration!
Herbert Van de Sompel, Los Alamos National Laboratory
