Tag clouds in the OPAC: a starting point

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See also Social media | Social cataloguing | Social tagging | Users of health libraries

Tag clouds in the online public access catalogue (OPAC) is a way of visually displaying subject tags using variations in font, type and colour to communicate the content in library collections or supplement it somehow. Tags and tag clouds are typically used in library OPACs to add to traditional subject analysis. The tagging of library resources can improve user discovery and navigation as tags have been shown to supplement subjects not covered by traditional subject headings [1].

Relationship between tags and tag clouds

What are tags?

  • Tags are keywords used to describe resources. Tags may be used to categorize, retrieve, and compare resources and are user-generated (versus based on controlled vocabulary). In OPACs, tags are most often applied by the library rather than by users [2]

What are tag clouds?

  • Tags may be arranged alphabetically, by frequency of use, or chronologically to form tag clouds, which are displayed using a paragraph layout or other formations. Often, only a portion of the tag cloud is displayed to the user.
  • Terms in a tag cloud may be hyperlinked, so users can access resources tagged with that term by clicking on it.

Tag clouds and searching

Source: Google images
  • A tag cloud can help users quickly get a visual sense of content and focus at a site, and the common terminology used.
  • Varying font sizes, weights, and/or colours helps readers distinguish between more and less frequently used tags. These features can reflect the tag’s popularity, how often a tag is used for a single item, the number of items given that tag its relationship to other tags or to the content it describes. Generally, the largest tag presents the most popular or frequently used tag (p.916).[3]
  • Libraries can add tags and tag clouds to their OPACs to enhance search capabilities. Tags are generally used in addition to traditional subject access (such as Library of Congress subject headings),and have been shown to improve findability in the OPAC.[1]
  • Users can navigate using tags in much the same way they navigate with traditional subject headings; hyperlinked tags take them to more resources that share the same tag.

Tag clouds, pros & cons


There are many benefits to the use of tags in OPACs:

  • User-generated content; user-friendly and less formal than subject headings.
  • A "minicatalog of resources" (p. 19)[4].
  • Make OPACs more interactive and responsive, increase value of OPACs.
  • Social and create community; can be created from the list of tags.
  • Increase "findability" (p. 59)[5] and supplement traditional means of accessing information.
  • Source of bringing vernacular into controlled vocabularies.[2]
  • Reflect how users categorize information.
  • Allow more choices to identify content.


The disadvantages of tags have been identified as such:

  • Tags are often imprecise and do not consider the idea of specificity
  • Many tags are used in a non-standardized way, and similar tags may not be linked.
  • Difficult to maintain the consistency of content.
  • Words have multiple meanings, so some tags may be unintelligible.
  • Words are often misspelled; not controlled vocabularies.
  • Tag may have little or no meaning to other users; tags make page look crowded.
  • User tags by themselves cannot provide the best subject access to the materials in library collections. (p.182)[1]
  • Debatable if tagging is a passing trend or here to stay.

Tag clouds in the OPAC

There are a variety of ways that libraries can add tag clouds to their OPAC:

  • LibraryThing for Libraries is a catalog enhancement application that imports millions of user-created tags from LibraryThing directly into an OPAC, displaying tags as clouds beside traditional Library of Congress subject headings. See also LibraryThing.
  • Libraries can invest in a next-generation discovery layer that includes tag clouds; these interfaces sit atop the library's integrated library system, operating as the front-end of a library catalogue. Bibliocommons,Encore,AquaBrowser, and Primo are all discovery layers that offer tag clouds and tagging functionality.
    • Bibliocommons has created this short instructional video, showing how library staff can add tags to enhance user discovery.
  • Libraries can implement an open-source discovery layer to allow for tagging; one example is SOPAC (the social OPAC), a project that permits tagging, rating and reviewing.
  • Libraries can create their own discovery layer, including tag clouds, using free open-source software. This option requires a high degree of technical expertise, but gives libraries the ability to custom-create an interface that meets their needs.

Examples of OPACs using tag clouds


Natural language vocabulary applied as tags has its benefits: it is current, colloquial and captures changes quickly instead of waiting for amendments or additions to a controlled vocabulary. Tagging also allows users to understand terms as it reflects sociocultural background, or depth of subject knowledge. By adding tagging systems to OPACs, libraries create more potential access points, and users can see what libraries have to offer. Although a duplication of effort, libraries, in their role as information providers, aim to offer patrons as many tools and options as possible -- and, so it is with tagging in the OPAC.


  1. 1.0 1.1 1.2 Rolla P. User tags versus subject headings: can user-supplied data improve subject access to library collections? Libr Resour Tech Serv. 2009;53(3):174-184.
  2. 2.0 2.1 Thomas M. To tag or not to tag? Libr Hi Tech. 2009;27(3):411-434.
  3. Shiri A. An examination of social tagging interface features and functionalities: An analytical comparison. Online Info Rev. 2009;33(5):901-919. http://bit.ly/aniXjA
  4. Webb PL, Nero MD. OPACs in the clouds. Computers in Libraries. 2009;29(9):18-22.http://bit.ly/aQ8RX6
  5. West J. Folksonomies and tags. Library Media Connection. 2007;25(7):58-59.http://bit.ly/9s2Nsw
  6. Garza A. From OPAC to CMS: Drupal as an extensible library platform. Library Hi-Tech. 2009;27(2):252-267. http://bit.ly/9vzwrv

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