Is Precoordination Unnecessary in LCSH?
Are Web Sites More Important to Catalog than Books?

Precoordination of LCSH subject headings, both (partially) in the LCSH thesaurus and (more extensively) in OPAC browse displays, continues to be necessary for several reasons:

• The meaning of thousands of LCSH headings depends on their word order in ways that cannot be captured by postcoordinate Boolean combinations or by word proximity searches that drop relational prepositions as stop words.
• A vast network of linkages between LCSH headings and the LCC classification scheme depends on precoordination i.e., changes in the word order of the subject strings also changes the classification areas to which the terms point.
• Displays of precoordinated strings enable researchers to simply recognize whole arrays of relevant research options that they could never specify in advance in postcoordinate combinations. The larger the file, the more such recognition capabilities are necessary.
• The precoordination of terms is inseparably linked to a vast network of cross- references that would vanish without it.

Books are not vanishing or generally evolving into digital forms; they continue to be published in huge numbers every year, and they provide formats that are more readable for lengthy texts.

In the future, LCSH must serve in both the environments of online library catalogs and the Web not the latter in place of the former.

An Online CIP (OCIP) program would enable our profession to maintain the necessary precoordination of LCSH headings in OPACs and also to insert librarian-created LCSH elements into the Web headers of participating online publishers. This would enable us to exploit the existing precoordination and postcoordination capacities of OPACs, and also to exploit LCSH more extensively in the exclusively postcoordinate search environment of the Web.

LCSH headings in copy cataloging cannot be simply accepted "with little or no modification."

Library of Congress
January 23, 2001
Library of Congress Help Desk