Friday, November 05, 2010

Link Rot: DOIs, EZIDs, PURLs, and ARKs

The Chronicle of Higher Education has a Hot Type article on page A14, "Publishers Find Ways to Fight 'Link Rot' in Electronic Texts," by Jennifer Howard. In a previous article, the same author introduced her readers to the problem of link rot, with which librarians are all-too familiar. Then, in this article, she spends time discussing several interesting organizations set up to combat the problem.

The first is, which is a non-profit membership organization set up by scholarly publishers. On its website, CrossRef describes its mandate as publisher collaboration, make reference linking throughout online scholarly literature efficient and reliable. As such, it is an infrastructure for linking citations across publishers, and the only full-scale implementation of the Digital Object Identifier (or DOI) System to date.

What a DOI is:
A unique alphanumeric string assigned to a digital object – in this case, an electronic journal article or a book chapter. In the CrossRef system, each DOI is associated with a set of basic metadata and a URL pointer to the full text, so that it uniquely identifies the content item and provides a persistent link to its location on the internet.

For more information on the DOI itself, which is a NISO standard syntax, please visit the International DOI Foundation website at
Back to the Chronicle article, where author Howard cautions her readers with a blog post from Ars Technica, DOIs and their Discontents where John Timmer blogged that Digital Object Identifiers (DOIs) could be put out before the object linked was actually published, for instance, if an article were reviewed or written about and the DOI attached were included in the review, all before the item was actually released to the public.

Author Howard also notes that speaking with the people at CrossRef helped her understand how making citations permanently available is a collective problem that must be solved collectively. The networking nature of all the citations linking to each other means that you depend on everybody's links remaining in good conditions, not just your own.

CrossRef began with the hard sciences, and expanded into social sciences and the humanities. There are about 3,215 publisher members of the organization, and some libraries as well, who publish materials, policing one another to encourage good citizenship, to ensure nothing is lost. At the beginning, it was mostly large scholarly publishers, but now more smaller publishers seem to be joining, and more monographs are being added as well. But the smaller publishers have a harder time affording the costs of the DOIs. CrossRef offers tiered pricing for members.

But there are other options to avoid link rot. is another non-profit organization, more international in scope that produces DOIs for libraries and data centers. It seems very focused on the hard sciences, though the website emphasizes that DOIs manage any sort of data. One U.S. member of DataCite, the California Digital Library, has also developed its own in-house version, called EZID. EZIDs can be used to track things like datasets that have not usually been tracked before, as well as scholarly articles. PURLs, Persistent Uniform Resource Locators were the first solution I heard of to Link Rot. We are introduced to ARKs, Archival Resource Keys. Finally, she introduces Zotero, an extension of the popular Firefox web browser that allows users to gather, organize and store information and citations, formatting them and sharing them easily. But it also allows users to create an archival copy of the web page from which they did their research. This is an innovative way in which to combat link rot. The author does not actually report on Zotero, but merely mentions it.

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