About
Introduction
The Library of Congress Authorities and Vocabularies service enables both humans and machines to programmatically access authority data at the Library of Congress. This service is influenced by -- and implements -- the Linked Data 
movement's approach of exposing and inter-connecting data on the Web via dereferenceable URIs.
Terms of Service
The Library of Congress has prepared this subject terminology system and is making it available as a public domain data set. While it has attempted to minimize inaccuracies and defects in the data and services furnished, THE LIBRARY OF CONGRESS IS PROVIDING THIS DATA AND THESE SERVICES "AS IS" AND DISCLAIMS ANY AND ALL WARRANTIES, WHETHER EXPRESS OR IMPLIED.
Scope
The scope of the Authorities and Vocabularies service is to provide access to commonly found standards and vocabularies promulgated by the Library of Congress. This includes data values and the controlled vocabularies that house them. The main application provides resolvability to values and vocabularies by assigning URIs. Each vocabulary possesses a resolvable URI, as does each data value within it.
URIs accessible at id.loc.gov only link to authority data -- that is, controlled vocabularies and the values within them. Therefore, users will not find identifiers for electronic bibliographic resources. The Library of Congress uses other identifier schemes such as Handles for this purpose.
Goals
- The Library of Congress strives to communicate a clear usage policy for all vocabularies accessible through id.loc.gov. Particular emphasis is made to include vocabularies which Library of Congress already exposes without restriction on use.
- By minting a URI for either a vocabulary or an individual data value, the Library of Congress promotes these resources to first-class, dereferenceable web resources.
Which vocabularies are included?
The Library of Congress Subject Headings is the the first inclusion for the Authorities and Vocabularies service. This initial offering is an almost verbatim re-release of the system and content once found at the popular prototype lcsh.info service. The primary exception is the form of the URIs.
- Old:
http://lcsh.info/{identifier}- New:
http://id.loc.gov/authorities/{identifier}
If you have used the legacy lcsh.info metadata in an application, we advise updating to the new URIs, as we cannot guarantee a permanent redirect from old lcsh.info URIs to the new URIs at id.loc.gov.
LCSH in this service includes all Library of Congress Subject Headings, free-floating subdivisions (topical and form), Genre/Form headings, Children's (AC) headings, and validation strings* for which authority records have been created. The content includes a few name headings (personal and corporate), such as William Shakespeare, Jesus Christ, and Harvard University; and geographic headings that are added to LCSH as they are needed to establish subdivisions, provide a pattern for subdivision practice, or provide reference structure for other terms. This content is expanded beyond "the big red books" (the paper issue of LCSH) with inclusion of validation strings.
*Validation strings: Some authority records are for headings that have been built by adding subdivisions. These records are the result of an ongoing project to programmatically create authority records for valid subject strings from subject heading strings found in bibliographic records. The authority records for these subject strings were created so the entire string could be machine-validated. The strings do not have broader, narrower, or related terms.
The Library of Congress will also release additional vocabularies, including:
- Thesaurus of Graphic Materials
- MARC Geographic Area Codes
- MARC Language Codes
- MARC Relator Codes
Several additions in support of technical metadata standards will be:
- Preservation Events
- Preservation Roles
- Cryptographic Hash Functions
How it works
Users and machines simply request the URI of interest over HTTP. For example, to access the data value "World Wide Web" in the Library of Congress Subject Headings, one would request this URI:
When requesting this URI, users have mechanisms for specifying how they want to serialize the data they wish to access. These include common RDF serializations carrying Simple Knowledge Organization System (SKOS) metadata, and Javascript Object Notation (JSON).
See the Technical Center for more details.
Benefits
For users (whether human or machine):
- Access to data at no cost.
- Granular access to individual data values.
- Ability to download entire controlled vocabularies and the values within them in numerous formats.
- Ability to link to Library of Congress data values within your metadata via Linked Data.
- A simple interface based on Representational State Transfer (REST) that requires nothing more than requesting a resource over HTTP.
- Clearly stated licensing and usage policies for each vocabulary.
- A unified endpoint that enables users to access data from across Library of Congress divisions.
- Ability to visualize relationships between concepts and values.
For the Library of Congress:
- Minting data values maintained by the Library of Congress in the domain of loc.gov allows us to establish provenance when used in Linked Data or the Semantic web.
- Simpler bulk download mechanisms will save our systems from being taxed by convoluted download methods employed by users trying to access our data one record at a time.
- Provides an opportunity to convey best practices and lessons learned for guiding other organizations on how to convert and share their data as Linked Data.
Linked Data Disclaimer
Concepts within Library of Congress Authorities and Vocabularies assert relationships to similar concepts found in non-Library of Congress authorities and vocabularies whenever possible. These assertions are essentially made through linking via URLs to concepts found on the World Wide Web maintained outside of the Library of Congress. Because the target URLs are hosted by another institution, the Library of Congress cannot guarantee that these links will resolve successfully.
For example, the TELplus project offers a service that uses SKOS to provide RAMEAU subject headings as Linked Data . Library of Congress Subject Headings concepts within the Authorities and Vocabularies service include links to associated RAMEAU concepts found in the TELplus service. The RAMEAU service is in the early stages of development and the URIs may not always resolve in the coming months.
