Library of Congress

Authorities & Vocabularies

The Library of Congress > Linked Data Service > About: Main


The Library of Congress Linked Data 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 vocabulary 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.


The scope of the Linked Data 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 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.


  • The Library of Congress strives to communicate a clear usage policy for all vocabularies accessible through 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 authorities and vocabularies currently included in this service are listed on the Linked Data Service main page.

The Library of Congress will continue to release additional vocabularies, including those that support PREMIS, MARC, MODS, METS, and MIX.

How it works

Humans: a web interface is provided with search capability for individual vocabulary values. It supports instant download of hte metadata for the value with a choice of serializations. Machines: 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, machines 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.


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 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.