Monday, July 21, 2008

The Future of Subject Access in the 21st Century

Monday, July 14, 2008
4:00 - 5:15pm

Dr. Barbara Tillett
Chief, Cataloging Policy and Support Office, Library of Congress

Dr. Lois Mai Chan
Professor, School of Library and Information Science, University of Kentucky

Coordinated and moderated by Rhonda K. Lawrence

It was a great pleasure to hear these two accomplished women address the mystifying issue of how cataloging may be brought in line with current trends while at the same time retaining the positive aspects.

In her presentation, Dr. Tillett reviewed the LC assessment of the pros and cons of pre- versus post-coordination of Library of Congress Subject Headings (LCSH) and resulting changes that are being implemented at LC. The entire report and appendices can be found on the web at

  • Pre-coordination combines elements into one heading in anticipation of a search of that compound heading
  • Post-coordination combines headings or keywords at the time of search by user

Pros of pre-coordination include context, precision, and suggestibility.

Cons of pre-coordination include training time, syntax not understood by end users, headings too specific and many used only once, syndetic or connecting structure not rigorous enough, and slow incorporation of new terms.

Cons of post-coordination include limitations for recall and precision, poor relevance ranking capabilities, and less understanding (without the context of the string).

The recommendations of the LC report, some of which have been implemented, included:

  • Continue pre-coordinated strings
  • Assist end-users through improved "front-end" to OPAC including social tagging experiments
  • More automation of LCSH with software to suggest and verify subject headings
  • Simplification by removing the language subdivision which is already in fixed and variable fields
  • Utilize some form subdivisions in separate 655 (i.e. genre/form test with motions picture/tv currently being done)
  • Offer LCSH in a Simple Knowledge Organization System (SKOS)

For the future, Dr. Tillett predicted that the global use of LCSH will expand and that the process will be improved to reduce costs and at the same time maintain the system.

In her presentation, Dr. Chan offered her suggestions for changes to LCSH which would be theoretically sound but at the same time be more useful to OPAC and web users. These ideas can also be found in her paper in the appendices to the LC report at

Dr. Chan contrasted keyword - the predominant way to retrieve information on the web - with controlled vocabulary - the primary way for subject retrieval in library catalogs and many online databases. She outlined the many advantages of LCSH including richness, comprehensiveness, standardization, and translation into many languages. Her question is -- how can LCSH be made more flexible?

Challenges for the continued viability of LCSH included improving compatibility with other controlled vocabularies, simplifying rules for heading construction, improving tools for automatic indexing, and striving for interoperability with other retrieval languages.

In order to do this Dr. Chan recommended that the terminology be separated from the application by reconfiguring LCSH into two separate files:

  • The source vocabulary consisting of building blocks for subject cataloging and removing subject heading strings
  • A validation file which has a list of validated subject heading strings, a keyword-searchable file created from 6xx fields, a browsing tool, and is maintained by updating subject headings in the source terms

Advantages of a source vocabulary would include easier maintenance, compatibility with other controlled vocabularies, amenability to different applications in organizations, easier translation to other languages, facilitating automatic assignment of subjects, and more compatibility with user-assigned terms and social tagging.

Advantages of a validation file would include increased productivity by easily accessible ready-made subject headings, higher rate of correctly constructed subject heading strings, and facilitating end-user browsing and searching by showing search terms in their proper context in the string.

Dr. Chan looked at the advantages and disadvantages of social tagging. The positives of user participation and empowerment are tempered by the inability to represent complexities which will become more of a problem as content scale increases (example of Flickr with 6000 pictures tagged as "summer vacation"). She suggested improving social tagging by suggesting LCSH subject headings to users during tagging and by mapping user-assigned tags to LCSH.

The lively discussion at the Roundtable following the presentation suggested that many of us are realizing changes are necessary, and are becoming engaged in the conversation. It was encouraging to see that leaders in the field are doing some creative thinking about options and stimulating discussion of some potentially reasonable, but not simple to implement, options for the future.

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