The subject browsing on The Online Books Page is based on the Library of Congress Subject Headings (LCSH), as published at the Library of Congress Linked Data Service, with some enhancements and modifications.
Along with the existing relationships to broader, narrower, and related headings published by the Library of Congress (LC), we include additional relationships in order to improve browsing, and make it easier to find and cluster related subjects. For example, many alphabetically or lexically close headings for which LCSH does not explicitly publish relationships get linked in our browsing views. We also may relate subjects that appear to have geographical features in common, similar subdivisions, or that commonly occur together in library catalog records.
Most of these enhancements are made automatically, but some are added (or occasionally deleted) manually. Please let us know if there are additional relationships between subjects that would be useful to add, or relationships we've included that appear to be irrelevant or distracting.
For the most part, we aim to use the most up to date preferred headings the Library of Congress uses for its subjects, and to update our headings soon after the Library changes its preferred headings. However, in a few cases we have decided not to update to the most recent heading preferred by the Library of Congress, but instead use a heading that LC previously preferred. (In those cases, we will make LC's currently preferred heading an alternate heading here, so you can still find cross-references from their more recent heading.)
Specifically, for certain natural geographic entities (such as mountains, valleys, rivers, and bays) we may decline to update our preferred heading when the heading change results from a government order that has bypassed the usual public consultation process on their names (such as described in this guide), and when the prior name prevails in common use. Our reasons for doing this are summarized in this blog post.
We are currently using former Library of Congress preferred headings for the following subjects:
We also follow these usages in other subject headings based on the ones above, such as headings with subdivisions that use these geographic entities, whether or not there is an LC ID specifically defined for them.
When we import catalog records from other online libraries into our extended shelves (as described here), their headings will be automatically converted to our preferred headings when applicable.
When we link to searches in other libraries' catalogs (as described here), we assume those catalogs use the current Library of Congress subject headings, unless we've been informed otherwise. We will therefore convert our preferred headings back to current LC preferred headings for those searches when applicable, unless we know a library prefers other headings. Please let us know if you are using different headings (whether the same ones we use or others) in place of specific current Library of Congress headings, and we can accommodate them in our search links, and publish your preferences in our Forward to Libraries local map. (For more about these local accommodations, see our blog post From Our Subjects to Yours.)
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Edited by John Mark Ockerbloom (onlinebooks@pobox.upenn.edu)
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