LTI's approach to NLM MeSH, LC Children's, and Genre/Form heading authority control parallels procedures for LCSH headings. Separate files of authorized headings are maintained for each controlled vocabulary.
NLM MeSH Headings
Using the National Library of Medicine's MeSH authorities file, LTI offers a MeSH authority control service to medical and health sciences libraries. NLM headings are updated annually. Topical (650) and a few geographical (651) subject headings having a second indicator of 2 are extracted for MeSH processing. Major and minor descriptors, as well as subheadings, are included in the MeSH file. Conversion of MeSH to LCSH is not an option. Libraries not using MeSH headings may choose to delete them from bibliographic records.
LC Children's Subject Headings
In 1996 LC began distribution of Children's authority records based on Library of Congress usage. These headings supplement LCSH, providing alternative terms to simplify the adult terminology. Authority records in this short list are primarily topical (650) with a handful of simplified names (600, 610). In addition, bibliographic records may contain LCSH headings tagged as LC Children's headings but considered appropriate for children's use. Therefore, LC Children's headings are first matched against LC’s file of Children's authority records, and then against standard LC subject and name authority files.
Given that conflicts do occur between LCSH and LC Children's headings (e.g., LCSH Swine versus the LC Children's Pigs), libraries may want to consult with their ILS vendor about the desirability of integrating the two controlled vocabularies in a single index.
LTI offers four options for processing LC Children's headings:
When Children’s headings are converted to LCSH, second indicator codes of 1 in 6XX fields are changed globally to 0 and the appropriate subject subdivisions Juvenile literature, Juvenile fiction, etc. are added to the converted headings. Following authority control, resulting duplicate headings are removed from records. For example, a catalog record has these subject headings:
650 0 $aFishes$vJuvenile literature.
650 1 $aFishes.
Following authority control two identical LCSH headings will exist: $aFishes$vJuvenile literature. One of these headings will be deleted in a final LTI check.
Children's headings having no LCSH equivalent--e.g., French language materials--are retained, though the second indicator is still set to 0.
Sears Subject Headings
While Sears subject headings may be authorized using a file of Sears authority records,
the structure of Sears Subject Headings differs substantially from that of LCSH. Having both LC and Sears headings in a library’s database can create confusion because of the inherent conflicts and inconsistencies. To avoid this, LTI recommends that libraries with a substantial number of Sears headings choose the processing option that converts Sears headings to LCSH.
Genre/Form Heading Processing
Genre headings in 655 fields are authorized using LTI's Genre Heading processing option. Headings may include LCGFT (Library of Congress genre form terms) or NLM MeSH. Libraries have the option to convert GSAFD (Guidelines on Subject Access to Individual Works of Fiction, Drama, Etc.) headings to LCGFT. LTI may authorize additional genre/form controlled vocabularies in the future when demand and authority record availability warrant it.
Implementation of genre/form headings has taken many years and several forms since first announced in 2007. LC’s original approach was to identify LCSH headings that describe forms or genres for use in a field tagged: 655 _7 … $2lcsh. Later, to parallel subject heading use, the tagging was revised to prefer: 655 _0, with no $2. In 2010, LC announced that it would, instead, create a new thesaurus for genres and forms, to be called Library of Congress Genre/Form Terms for Library and Archival Materials (LCGFT). Headings taken from this list are assigned as: 655 _7 … $2lcgft. The following year, LC replaced all the form/genre authority records that had been issued using the control number prefix sh with new records using the prefix gf.
In authority control processing, 655 headings with fields tagged in any of the above forms (655 7 … $2lcsh, 655 0 [no $2], or 655 7 … $2lcgft) are pulled from bibliographic records for processing. Headings are compared against LC's genre/form (gf) authority records and LTI-created authority records derived from official and semi-official sources. Content of the headings is updated to current usage, including correction of typographical errors in entry. If $2 is absent, but the code is present following a space, headings will still be pulled, e.g. $aAerial photograph lcgft will be recognized and $2 inserted as $aAerial photograph$2lcgft. A variety of typos are also corrected: $2lcgtf, $2lgft, etc. are corrected to $2lcgft. All LC-derived headings are converted to 655 _7 …$2lcgft, reflecting current usage. Authority records for all form/genre headings that have a record are provided to libraries in a separate file.
In late 2015, LC completed a project to create authority records for general, music, and literature genre/form terms. Despite, this, there remain some terms originally identified in LCSH but not yet represented by national authority records. LTI has supplemented the official headings with some 655 terms that are authorized as LCGFT although they lack authority records. Unless otherwise instructed, LTI tags these terms in the same manner (655 7… $2lcgft).
Some libraries may still be using the GSAFD thesaurus for genre/form terms. This thesaurus has not been updated since 2001, and the majority of terms are now covered by LCGFT headings. LTI strongly recommends conversion of GSAFD terms to LCGFT.
Prior to the implementation of genre/form headings, many libraries assigned the corresponding terms in LCSH as topical subject headings. For example, to aid access to videos, many libraries assigned the topical heading Videorecordings in a 650 field. LTI offers an additional option to convert such headings to 655 fields using the current LCGFT term. The latter conversion occurs only with stand-alone $a genre/form headings. If an LCSH topical heading includes another subfield, such as $v, $x, $y, or $z, the heading is not considered a form heading.