Achieving Link Integrity for Managed Collections

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Thor Conference, Rome, Italy, November 15 2017
Herbert Van de Sompel
Los Alamos National Laboratory
@hvdsomp
Achieving Link Integrity for Managed Collections
Photo by Eric Sieverts

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Hyperlinks in Theory

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Hyperlinks in Reality

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Link Rot

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Content Drift

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Content Drift
2000 2004
2005 2008
http://dl00.org in 2000, 2004, 2005, 2008

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Content Drift
http://icecube.wisc.edu/ on May 8 2009 (left) and August 27 2009 (right)

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No Content Drift
http://www.ifa.hawaii.edu/~cowie/k_table.html on June 9 1997 (left) and March 2016 (right)

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The Web, All Hyperlinks Subject to Link Rot, Content Drift

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The Web, All Hyperlinks Subject to Reference Rot
• Reference Rot hinders our ability to follow links as they were
intended when they were put in place:
• Link rot: A link stops working all together
• Content drift: The Linked content changes over time and may
eventually no longer be representative of the content that was
originally linked

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Creating Pockets of Persistence
• How to maintain the integrity of links?
• This challenge exists for the entire web. Some communities with well
managed collections care about addressing it because they consider
it a Quality of Service issue:
• Scholarly communication
• Cultural heritage
• Legal publications
• Government communication
• Journalism
• Wikipedia
• …
• What can these communities do to create Pockets of Persistence?

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A Managed Collection Desires Reliable Outlinks

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Links to another Managed Collection

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Links to Web at Large Resources

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Exploring Link Rot & Content Drift

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<Intermezzo - Hiberlink Study re Reference Rot in STM Articles>

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PubMed Central Corpus
PMC articles published 1997-2012 PMC
Total 479,194
With links to articles 240,857
With links to web-at-large resources 156,160
Links PMC
To articles 744,678
To web-at-large resources 480,853A B
A B

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Links to Articles & to Web At Large Resources - PMC
Martin Klein, Herbert Van de Sompel, et al. (2014) Scholarly context not found. In: PLOS ONE
https://doi.org/10.1371/journal.pone.0115253

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Links Rot Occurs when B moves to C

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Introduce PID(B)

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Link to PID(B) ; HTTP Redirect from PID(B) to B

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When B moves to C: HTTP Redirect from PID(B) to C

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Core Assumption: PID(B) Will Be Used for Linking

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Herbert Van de Sompel, Martin Klein, and Shawn Jones (2016) Persistent URIs Must Be Used
to Be Persistent. In: WWW2016. http://arxiv.org/1602.09102

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• When classifying links extracted from PMC as linking to articles, we
assumed that filtering on http://dx.doi.org/* would do the trick
• But we found a lot of e.g. http://link.springer.com/article/*
• For example:
• http://link.springer.com/article/10.1007%2Fs00799-014-018-0
• Instead of:
• http://dx.doi.org/10.1007/s00799-014-0108-0
• We used CrossRef’s Reverse Domain Lookup to classify these
extracted links as linking to articles
A Disconcerting Observation

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URI References - PMC
Herbert Van de Sompel, Martin Klein, and Shawn Jones (2016) Persistent URIs Must Be Used to Be Persistent.
In: WWW2016. http://arxiv.org/1602.09102
Herbert Van de Sompel, Martin Klein, and Shawn Jones (2016) Persistent URIs Must Be Used
to Be Persistent. In: WWW2016. http://arxiv.org/1602.09102

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Cartoon by Patrick Hochstenbach
http://signposting.org
<Intermezzo – Signposting the Scholarly Web>

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• Proposal:
Use typed links to address some long standing problems regarding
scholarly resources on the web, by interlinking them using
appropriate relation types
• Focus on a limited set of patterns to support uniformly:
•Conveying a Persistent Identifier
•Expressing the web boundary of a scholarly resource
•Making bibliographic metadata discoverable
•Conveying an Author Identifier
•Conveying a license that applies to a resource
•Conveying a resource type
Signposting the Scholarly Web

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HTTP Links
Mark Nottingham (2017) RFC8288: Web Linking
http://tools.iets.org/rfc/rfc8288.txt

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HTTP Links

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HTTP Links Are Used
curl –I http://dbpedia.org/data/Reykjavik
HTTP/1.1 200 OK
Date: Thu, 27 Oct 2016 04:43:28 GMT
Content-Type: application/rdf+xml; charset=UTF-8
Content-Length: 1210
Link:
<http://creativecommons.org/licenses/by-sa/3.0>
; rel=“license",
<http://dbpedia.org/data/Reykjavik>
; rel="alternate"; type="text/n3",
<http://dbpedia.org/resource/Reykjavik>; rel="describes",
<http://mementoarchive.lanl.gov/dbpedia/timegate/http://dbpedia.org/
data/Reykjavik>
; rel="timegate"

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For PIDs: Use cite-as Relation Type
Van de Sompel, H., Nelson M., Bilder, G, Kunze, J., and Warner, S. (2017) “cite-as”: A Link Relation
to Convey a Preferred URI for Referencing https://datatracker.ietf.org/doc/draft-vandesompel-citeas/

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• The target URI (PID) of the cite-as link can be picked up by
applications, e.g.:
• reference managers can pick up the PID of an object when the
user saves it while on the landing page, one of the constituent
resources
• publication pipelines can pick up the PID by looking up (HTTP
HEAD) URIs referenced in a paper to determine whether a PID
exists for them
For PIDs: Use cite-as Relation Type

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Cartoon by Patrick Hochstenbach
http://signposting.org
</Intermezzo – Signposting the Scholarly Web>

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PID Alternative - When B Moves to C: HTTP Redirect from B to C

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PID Alternative - When B Moves to C: HTTP Redirect from B to C
• Custodian of C needs to hold on to domain of B
• Custodian of C needs to establish redirection patterns; often those
are rather simple rules
• No problem with establishing links to PID(B); the URI in the browser
address bar (initially B, later C) is just fine

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Content Drift Occurs when B Changes over Time

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Content Drift Occurs when B Changes over Time
• Is not really considered an issue because:
• the objects that receive PIDs were typically static, e.g. scientific
papers
• when a (substantially) new version of an object is published,
typically a new PID is assigned
• But:
• how to verify that the retrieved version of an object is indeed the
referenced version of the object?
• Requires:
• archiving objects in trusted archive(s)
• ability to retrieve objects from the archive(s)

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Archived Articles
David Rosenthal (2013) Patio Perspectives at ANADP II: Preserving the Other Half
http://blog.dshr.org/2013/11/patio-perspectives-at-anadp-ii.html
Too few
Too low risk

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How to Audit Whether a PID-identified Object is Archived
http://thekeepers.org
Journal,
Volume, Issue
centric
Global audit by
DOI?

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Contrast: All Web-Archived Versions of David’s Blog Post
Global audit by
HTTP URI
Uses Memento
infrastructure
http://timetravel.mementoweb.org

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Scholarly Context Adrift
Shawn Jones, Herbert Van de Sompel, et al. (2016) Scholarly context adrift. In: PLOS ONE

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How to Assess Content Drift?

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Step 1: Find Pre/Post Mementos

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Step 2: Select Representative Mementos

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Text Similarity Measures
• Compute aggregate text similarity scores (values between 0...100)
for:
• Simhash
• Jaccard
• Sørensen-Dice
• Cosine
• If the aggregate score is 100, we decide that the Pre/Post
Mementos are representative
• We find 137K URI references out of 480K that have representative
Mementos

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Step 3: Dereference Live Web Version of URI

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Step 4: Representative Memento vs. Live Version

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Content Drift - PMC

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Reference Rot for Links to Web at Large is Severe
• Link Rot and Content Drift are severe
• Cannot retrieve originally linked content from the live web
• Can potentially retrieve originally linked content from web archives
• But the archival coverage is too poor, a result of incidental
archiving

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URI References without Representative Mementos - PMC

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Impact of Archival Gap on Links from Managed Collections
Martin Klein, Herbert Van de Sompel, et al. (2014) Scholarly context not found. In: PLOS ONE
Links from Managed Collections to Domains Grey: Linked Content not Archived

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Uncertainty Regarding the Future of B when A Links to It

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Custodian of A Takes a Snapshot of B when Linking to It

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Taking a Snapshots of B: Automation is Key
• Web archive APIs for on-demand archiving
• perma.cc, Internet Archive, archive.is, webcitation
• Amber for Wordpress & Drupal archives resources linked in a page
• http://amberlink.org/
• Hiberlink’s experimental Zotero extension archives bookmarked
URLs
• http://hiberlink.org/zotero.html
• Hiberlink’s experimental HiberActive archives all URLs referenced in
a newly submitted paper
• https://www.slideshare.net/martinklein0815/hiberactive

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site2cite
http://site2cite

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Custodian of A Links to Snapshot of B
• Typical practice for linking to snapshots:
<a href=“URL of snapshot of B”>
• Problems with this practice:
o Impossible to visit the original URI, if desired
o Requires the permanent existence/uptime of the archive that
holds the snapshot
-One link rot problem replaced by another
http://robustlinks.mementoweb.org/about/

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Permanent Existence/Uptime of Archives?
Capture of http://webcitation.org dated July 17 2013
https://archive.today/eAETp

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Remnant of discontinued web archive http://mummify.it captured on February 14 2014
https://web.archive.org/web/20140214233752/https://www.mummify.it/

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http://www.themoscowtimes.com/news/article/russia-bans-wayback-machine-internet-archive-over-
islamic-state-video/510074.html

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http://web.archive.org/web/20121101043952/http://vogin.nl on March 6 2017 at 15:59 CET

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Custodian of A Links to Snapshot of B, Decorates the Link
• Desired practice for linking to captures is to decorate the link so it
provides a variety of options:
<a href=“URL of snapshot of B”
data-originalurl=“B”
data-versiondate=“datetime of snapshot of B”>
• Supports:
o Revisiting the original URL
o Finding snapshots in any web archive (via original URL)
o Finding a temporally appropriate snapshot in any web archive
(via original URL & snapshot datetime)
o Automatically accessing a temporally appropriate snapshot in
any web archive (Memento protocol using original URL &
snapshot datetime)
http://robustlinks.mementoweb.org/spec/

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Robust Links: Link Decoration in Action
See Robust Links at work in: Van de Sompel H. & Nelson, M.L. (2015)
Reminiscing about 15 years of interoperability efforts. D-Lib Magazine.
https://doi.org/10.1045/november2015-vandesompel
JavaScript makes the
link decorations actionable
Robust Links Javascript
https://github.com/mementoweb/robustlinks

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Recap - A Managed Collection Desires Reliable Outlinks

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Takeaways
• When it comes to links to
managed collections, the
custodian of the linking collection
relies on the custodians of the
linked collections to preserve link
integrity.
• PIDs, HTTP redirects are
managed by the custodian of
linked collections.

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Takeaways
• When it comes to links to web at
large resources, the custodian of a
linking collection cannot rely on the
custodians of those linked
resources to maintain link integrity.
• Creation of Mementos, Robust
Links is managed by the custodian
of the collection that links to web at
large resources.

Achieving Link Integrity for Managed Collections

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