Two great sources of information for Library of Congress Subject Headings (LCSH) can be found online. Both are based on information from the LCSH authority files maintained by the Library of Congress.
1.) “id.loc.gov” is maintained by the Library of Congress. It is the Library of Congress’ foray into open and shareable authority data.
URL: http://id.loc.gov
Sample record: Online chat groups: http://id.loc.gov/authorities/subjects/sh97004058.html
Features: Scope note at top of record (when available), list of variants terms, and lists of broader, narrower, and related terms. A great feature is that the broader, narrower, and related terms are hyperlinked to the records for those terms. Note the tab for visualization, too, for those who want a visual view of relationships.
id.loc.gov also provides access to LC Children’s Subject Headings, LC Genre/Form Terms, etc.
2.) ZVON
URL: http://zvon.org/lib/lcsh/index.html
Sample record: Online chat groups: http://zvon.org/lib/lcsh/index.html#sh97004058
Features: Much like id.loc.gov, ZVON provides a scope note at the top of each record when it’s available and a list of variant terms. In addition, ZVON provides an interactive hierarchy within each record and has a very user friendly search interface.
ZVON also provides a number of other resources useful to librarians, such as a Library of Congress Classification Outline, a Project Gutenberg browser, and a Dublin Core and DCMI metadata reference. The Resources for Librarians page can be found here: http://zvon.org/lib/
For more information please contact Jackie Blonigen or Felicity Dykas.