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Tags are keywords chosen by users of a system to describe an item (e.g., a website or book).  Tags gained popularity at Web 2.0 sites like Delicious, Flickr, and LibraryThing, and have now begun to appear in a few library catalogs.  Tags, which usually consist of single words but can extend to short phrases in some systems, offer an alternative to the assignment of subject headings in traditional cataloging.  There are four strategies libraries can pursue with respect to the relationship of tags to subject headings, in order of most conservative to most radical: Ignore tagging and continue to exclusively use subject headings; allow tags to Coexist with subject headings, but maintain a clear boundary between the two; utilize tags and subject headings side-by-side, permitting each to inform the other (Cooperate); or deprecate subject headings and Replace their function with tags.

At a bare minimum, tags allow “patrons to personalize the library’s website” (Rolla, 2009, p. 175).  Patrons—and catalogers and other staff—can use tags to bookmark, review, group, and annotate items in the catalog.  Beyond direct value to their creator, tags gain additional value when systems aggregate large numbers of user tags.  Like many other examples of Internet technology, when drawing on a large pool of users the simple system of tagging displays emergent properties—the overlap between users’ personal tags creates an informal shared vocabulary, or folksonomy.  Folksonomies automatic incorporation of current and natural terminology is another advantage over controlled vocabularies, which are by definition frozen and in practice often stilted (Rolla, 2009).  Additionally, the number of times an item is tagged provides a direct indication of its popularity and, by extension, a measure of its value (“Social bookmarking,” 2010).

A user tagging a book has a natural advantage over catalogers—the user is likely to have read the book, unlike the cataloger (Rolla, 2009).  Users “assign many more tags to books than library catalogers assign subject headings. … Catalogers, by following the Library of Congress guidelines [to only identify primary subjects], may omit concepts that are important to users” (Rolla, 2009, pp. 177-178).  In his 2009 study of LibraryThing tags, Rolla compares tags in LibraryThing with subject headings in the Library of Congress (LC).  Rolla finds that tags identify concepts ignored by the Library of Congress Subject Headings (LCSH), including both broader terms and narrower terms (2009).

Maintaining a controlled vocabulary like LCSH is extremely difficult and resource intensive, and cataloging with and using LCSH properly requires training (Rolla, 2009).  LC, in fact, is taking steps to move away from pre-coordinated strings of subject headings (Mann, 2008).  Even though cataloging with subject headings is costly and despite the advantages tags can offer, research shows that subject headings have value that cannot be replaced by tags (Mann, 2008; Rolla, 2009; Steele, 2009; Thomas, Caudle, & Schmitz, 2009).  Folksonomies suffer from issues with ambiguous meaning (e.g., synonymy, polysemy, homonymy, etc.), “whereas one of the main purposes of controlled vocabularies is to disambiguate polysemous words and choose preferred terms from groups of synonyms” (Rolla, 2009, p. 175).  Replacing subject headings is not a viable strategy unless libraries are willing to seriously sacrifice cataloging quality.

On the other end of the spectrum, Ignoring tags is an equally poor option, as the value they can add to cataloging is clear.  Adding tags while retaining subject headings will markedly improve access (Rolla, 2009; Steele, 2009; Thomas et al., 2009).  Even Mann, always the staunch defender of traditional cataloging, calls for LCSH and tags to Coexist. Mann’s conclusion is that LC should accept tags but only in such a way that they are clearly separated from LC’s bibliographic records and catalog.  He would have LC expose its records to these linked sites but not pollute the core LC records and catalog with tags.  The coexistence option is exemplified by the University of Pennsylvania library:

PennTags allows members of the Penn community to tag web sites, articles in the library’s database, and records in both the video catalog and Franklin, the library’s OPAC. … Besides the “Add to PennTags” link, the tags are not on Penn Libraries’ OPAC itself.  Those more comfortable with the traditional search experience are not distracted by cloud tags or other unfamiliar features of tagging sites.  This way, the library caters to both those seeking a new way to interact with the catalog, and the traditional user. (Steele, 2009, p. 75)

On the other hand, not incorporating the tags into the base level OPAC means that tags are also hidden from OPAC users who might benefit from the tags’ functionality.  Only users who seek out the separate PennTags interface can benefit.

The Cooperate strategy is similar to coexistence, but incorporates tags directly into the library catalog.  Rolla (2009), Steele (2009), and Thomas, Caudle & Schmitz (2009) all conclude that tags can effectively supplement subject headings in catalogs.  Controlled vocabularies and folksonomies have complementary strengths and weaknesses.  Tags are easy to use, especially for quick searching, while subject headings can correct for tags’ ambiguity.  Subject headings are also indispensible for browsing by scholars in search of an overview of a topic (Mann, 2008).

“The benefit of tagging as a supplement to LCSH is more likely to occur when there are a large number of tags in the system” (Thomas et al., 2009, p. 430).  It’s not until we see tags shared on at least a large consortial level—better yet a national or international level—that network effects can kick in to produce unexpected results.  The future of tagging in libraries hinges on this point: will tags be shared globally (via LC, OCLC, or some other institution/mechanism), like other bibliographic information?  Even in the presence of such a global system, some libraries will opt to constrain their local catalogs to only local tags, or may continue to ignore tags altogether, but libraries as a whole (and therefore library users and society as a whole) stand to benefit from a shared namespace for tags.

Mann, T. (2008). “On the record” but off the track: a review of the report of the library of congress working group on the future of bibliographic control, with a further examination of library of congress cataloging tendencies. Retrieved from http://www.guild2910.org/WorkingGrpResponse2008.pdf

Rolla, P. J. (2009). User Tags versus Subject Headings: Can User-Supplied Data Improve Subject Access to Library Collections? Library Resources & Technical Services, 53(3), 174-184.

Social bookmarking. (2010, March 28). In Wikipedia, the free encyclopedia. Retrieved April 13, 2010, from http://en.wikipedia.org/wiki/Collaborative_tagging

Steele, T. (2009). The new cooperative cataloging. Library Hi Tech, 27(1), 68-77.

Thomas, M., Caudle, D. M., & Schmitz, C. M. (2009). To tag or not to tag? Library Hi Tech, 27(3), 411 – 434. doi:10.1108/07378830910988540

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