The failure of a web address to link to the appropriate online source is a significant problem facing scholarly material. Martin Klein and Herbert Van de Sompel together with their collaborators have investigated the extent of reference rot on scholarly domains and their results show an alarming link rot ratio. The authors also explore ways to mitigate it through more systematic web archiving practices and link decoration techniques

Klein, Martin

Van de Sompel, Herbert

LSE Research Online

2/5/2015Reference rot in web-based scholarly communication and linkdecoration as a path to mitigationblogs.lse.ac.uk/impactofsocialsciences/2015/02/05/reference-rot-in-web-based-scholarly-communication/The failure of a web address to link to the appropriate online source is a significant problem facingscholarly material. Martin Klein and Herbert Van de Sompel together with their collaborators haveinvestigated the extent of reference rot on scholarly domains and their results show an alarming linkrot ratio. The authors also explore ways to mitigate it through more systematic web archivingpractices and link decoration techniques.Referencing sources is a fundamental part of the scholarly discourse. This was true 50 years agoand still holds true today, even though, with the emergence of the web, scholarly communicationhas undergone a dramatic shift from a paper-based to a web-based endeavor. What has changed,however, is the variety of scholarly assets being referenced. Increasingly, we see references tosoftware, ontologies, project websites, presentations, blogs, videos, tweets, etc. Such resources areusually referenced by means of their HTTP URI as they exist on the web at large. These HTTPURIs allow for immediate access on the web, but also introduce one of the detrimentalcharacteristics of the web to scholarly communication: reference rot.We introduced the term reference rot as a combination of two problems common for URI references: link rot andcontent drift. Link rot represents the case where a URI ceases to exist and hence the request typically returns a “404– Page not found” response. Content drift describes the case where the resource identified by its URI changes overtime and hence, as time goes by, the request returns content that becomes less and less representative of what wasoriginally referenced.Our recent study, part of the research track of the Hiberlink project, investigates the extent to which science,technology, and medicine (STM) articles are subject to reference rot. Numerous link rot studies for the general webas well as for scholarly communication have been published over the years but the investigation into the aspect ofcontent drift as well as the sheer scale of our experiments make our study unique to date. We assembled threecorpora (arXiv, Elsevier, PubMed Central) consisting of more than 3.5 million scholarly articles published between1997 and 2012. Out of the 4 million URIs that we found (in about 1.8 million of the considered articles), more than 1million became subject to our analysis as they referenced web at large resources (blogs, project websites, etc.) asdescribed above. URIs that referenced STM articles were excluded from our study on the assumption that existingpersistent identifier and archival infrastructure makes such links immune to reference rot.Our results show an alarming link rot ratio for all three corpora: 13% of arXiv, 22% of Elsevier, and 14% of PMCarticles published in 2012 suffer from link rot. These numbers only increase for older articles, for example, forarticles published in 2005 the corresponding numbers are 18%, 41%, and 36%.1/4The graphic shows links from the three STM corpora that were studied (right hand side) tothe six top level domains they link to (left hand side). The colored portions shows links thatare healthy, the grey portions – by far the largest – show links that are infected by referencerot.We investigated the notion of content drift by checking for archival copies (Mementos) of the referenced web at largeresource in web archives. We considered a Memento created within 14 days of the article’s publication date asrepresentative to what was originally intended for the reference. While this time window is chosen somewhatarbitrarily, given the dynamic character of the web, we make the case that chances are fairly high that the referencedweb at large resource has changed within 14 days and hence does not necessarily represent the intended content ofthe reference anymore. Throughout all three corpora, about 75% of all URI references lack such representativeMementos.To elevate these numbers to the article level, we defined an article as being subject to reference rot if it contains atleast one URI reference that is either subject to link rot or is lacking a representative Memento. We extrapolated ourElsevier numbers to the scale of the overall STM article landscape and arrived at eye-opening numbers: about 20%of STM articles published in 2012 suffer from reference rot. The remaining 80% either do not contain any URIreferences or, when they do, they all still work and a representative Memento is available for each. Whenconsidering only those articles that contain one or more URI references, the ratio of infected articles published in2/42012 increases to 70%.Reference rot is clearly a significant problem, and, in addition to quantifying its extent, the Hiberlink project alsoexplores ways to mitigate it. The typical strategy to address the problem, followed by those who actually care aboutit, is as follows:When linking to a web page, a snapshot of the state of the page at linking time is created in a web archive.Several web archives provide on-demand snapshot functionality, including the Internet Archive, archive.today,and perma.cc.With the snapshot created, rather than linking to the original web page, a link to the snapshot is put in place.For example, we are writing this post on January 21 2015. And we want to link to http://www.w3.org/. That’s theW3C’s page, and it changes rather frequently. In order for future readers of this blog post to see the same W3Ccontent that we saw when linking, we create a snapshot, say in the archive.today web archive. That snapshot isavailable at https://archive.today/r7cov and, rather than linking to http://www.w3.org/, we link tohttps://archive.today/r7cov.While the creation of the snapshot is definitely an essential step in the right direction, there are problems with thelinking approach:Linking to the snapshot https://archive.today/r7cov, assumes that the archive.today web archive will existforever. Unfortunately, there are plenty of indications that web archives do not have eternal life either. If theweb archive in which we created the snapshot suffers a temporary glitch, moves its content to another weblocation, or ceases to exist, visiting the snapshot becomes impossible.When linking to the snapshot https://archive.today/r7cov, the URI of the W3C’s page, http://www.w3.org/, islost. As a result, future readers of this post cannot visit the W3C page to see its evolved state.Link decoration is a way to address these problems and to increase the chances that links will lead to meaningfulcontent, even a long time after they were put in place. In order to maximize link robustness, the following informationshould be available, in a machine-actionable manner, for a link:the URI of the snapshot, in our example https://archive.today/r7covthe URI of the original resource, in our example http://www.w3.org/the datetime of linking, in our example January 21 2015.The latter two information elements can be used to automatically find snapshots in other web archives in casearchive.today‘s service is interrupted, and the snapshot https://archive.today/r7cov becomes inaccessible as aresult.Discussions with interested parties are still underway regarding the best way to convey this information on a link.Until further notice, and for demonstrations purposes, the information is conveyed using HTML5’s attributeextensibility mechanism. Using that approach, this robust link to the W3C home page looks as follows:<a href=”http://www.w3.org/“data-versionurl=”https://archive.today/r7cov“data-versiondate=”2015-01-21″>this robust link to the W3C home page</a>The Memento Time Travel extension for Chrome makes these link decorations accessible when right-clicking on thelink. Try it with a version of the reference list of our above mentioned article in which links to web at large resourcewere decorated. For more information on link decoration, check out the Robust Links site.Note: This article gives the views of the author, and not the position of the Impact of Social Science blog, nor of the3/4London School of Economics. Please review our Comments Policy if you have any concerns on posting a commentbelow.About the AuthorsMartin Klein is an Analyst at the University of California Los Angeles Research Library. He can be found on Twitter@mart1nkle1nHerbert Van de Sompel is the team leader of the Prototyping Team at the Research Library of the Los AlamosNational Laboratory. The Team does research regarding various aspects of scholarly communication in the digitalage. He can be found on Twitter @hvdsompCopyright © The Author (or The Authors) - Unless otherwise stated, this work is licensed under a CreativeCommons Attribution Unported 3.0 License.4/4

Reference rot in web-based scholarly communication and link decoration as a path to mitigation

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