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Top > About Us > Electronic Library Projects > Standards for Digital Information > Use and Connect: What is NDL Linked Open Data (LOD)?

Use and Connect: What is NDL Linked Open Data (LOD)?

The National Diet Library (NDL) provides metadata as Linked Open Data (LOD) to facilitate effective use by computer systems or applications. This page provides general information about NDL LOD. Please refer to Use and Connect: How to use NDL LOD for the use of specific data or Use and Connect: How to link to NDL LOD for usage examples.

1. What is LOD?

Linked Open Data (LOD) is a method of publishing and sharing data on the web which is freely to available anyone (open license service) by connecting various data (Linked Data).
According to Tim Berners-Lee, inventor of the World Wide Web, the use of Linked Data should follow these four principles(1).

  1. Use Uniform Resource Identifiers (URI)s as names for things.
  2. Use HTTP URIs so that people can look up those names.
  3. When someone looks up a URI, provide useful information, using standard formats like RDF or SPARQL.
  4. Include links to other URIs so that users can discover more things.

The application of these principles allows related things such as titles, authors, places, and concepts to be linked to each other such that computers can identify their relationships.
The volume of Linked Data being published both in Japan and around the world is on the increase. At the G8 summit held on 18 June 2013, leaders of the G8 agreed to abide by the Open Data Charter, which sets out principles for releasing government data in a machine-readable and open format under open license(2).
Even prior to this development, national libraries in many countries had been providing LOD proactively(3) (4) (5). And events such as the LOD challenge have been held in Japan and many other countries to encourage the use of LOD worldwide(6).

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2. What is NDL LOD?

The NDL strives to provide the following LOD that meets the four principles described above and is open to everyone.

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Bibliographic Data (NDL Search)

Data Sources
Data Contents
  • Metadata of books, journals, articles, newspapers, digital contents (digitized materials, sounds, web pages etc.).
  • Metadata include title, author, publisher, subject matter (topics, geographic names), classifications (NDC, NDLC), ISBN, ISSN, National Bibliography No., the NDL call number, and information on holding libraries such as prefectural and municipal libraries.
  • NDLBibID (NDL Bibliography ID) which are used to identify bibliographic data that the NDL creates and provides and NDLJP (NDL permanent identifier) which are used to identify digitized contents and archival materials of Internet resources.
  • URLs of webpages which show digitized content (http://dl.ndl.go.jp/...)
  • Information related to copyright protection
    • *Tag value of dcterms:accessRights in digitized content including S02P99U99 (available via the Internet), S03P99U99 (available for print out), and S03P01U99 (not available for print out).
    • *Tag value of dcterms:rights includes Internet publication (termination of the period of protection), Internet publication (arbitration), and Internet publication (permission).
Terms for data description

The National Diet Library Dublin Core Metadata Description (DC-NDL) is used for data description. Please refer to Metadata for detailed information on metadata formats provided by the NDL.

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Authority data (Web NDL Authorities)

Data Contents
  • Information which identifies authors who have several names (pen names, maiden names, etc.) (e.g., Natsume Soseki and Natsume Kinnosuke) as well as synonyms (e.g., climate, climatic phenomenon, and weather)
  • Information which identifies different people with same names (e.g., Suzuki Ichiro, 1881–1961, and Suzuki Ichiro, 1900–1985)
  • Information on synonyms which indicate a certain topic (subject matter), hypernyms, hyponyms, and related words (e.g., synonyms, such as earthquake, seismic event, and tremor; hypernyms such as natural disaster, hyponyms such as earthquake fires, and related words such as seismic activity, earthquake insurance, and disaster prevention)
  • Family names (e.g., the Tokugawa clan, the Yamanouchi clan), and names of organizations (e.g., the National Astronomical Observatory of Japan, the Science Council of Japan)
  • Information on geographic name (e.g., Tokyo; Chiyoda-ku, Tokyo; Akasaka-ku, Tokyo; etc.)
  • URI (Link Data) of The Library of Congress Subject Headings (LCSH) and Virtual International Authority File (VIAF)
Terms for data description

The NDL uses SKOS-XL, SKOS, DC-NDL, RDFS, Dublin Core, FOAF and OWL as terms for authority data descriptions. Please refer to About the RDF Model 2. Vocabulary Used in the Authority Data for more detail.

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Earthquake related data (NDL Great East Japan Earthquake Archive (code name "HINAGIKU"))

Data Sources
  • Various institutional repositories which compile records about the Great East Japan Earthquake posted on List of repositories which metadata is available in "Application Programming Interface (API)" such as Geospatial Information Authority of Japan, Center for Remembering 3.11 (sendai mediateque), photos at the disaster area of Shinchi, Fukushima (Shinchi Municipal Library), ICT Project for Preserving Community Ties "Telling the Story of the Great East Japan Earthquake" (Higashimatsushima Library), Aerial photographs (by Aero Asahi Corporation), and the Web Archiving Project (WARP).
Data Contents
  • Metadata (title, creator, publisher, date, location, and summary/abstract) of photos (aerial photographs of the disaster area and photos of damage), sound recordings/videos (related to support activities for the affected areas, the Fukushima Daiichi nuclear disaster, and testimony of disaster victims, etc.)
    • *Ma:locationLatitude tag shows the latitude, ma:locationLongitude tag shows the longitude, and dcterms:created tag (in ndlkn:Resource class) includes the date of photos and movies.
  • Metadata (title, publisher, and saved date, etc.) of old web pages (municipal governments, etc.)
  • Metadata (title, creator, publisher, etc.) of books, journals, newspapers, and brochures (flyers, etc.).
  • URLs of webpages that show digitized content (documents, photos, sound recordings/movies), thumbnail URLs, and URLs of webpages which shows past webpages.
Terms for data description

Terms of the NDL's Great East Japan Earthquake Archiving Metadata Schemas are used for data description.

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3. Promotion of LOD by the NDL

NDL initiatives to promote LOD include the following:

Cooperative Research Project on making Linked Data of the Nippon Decimal Classification

The Nippon Decimal Classification (NDC) is a standard classification system developed and maintained by the Japan Library Association (JLA) for the efficient management of library collections in Japan. The NDL and the JLA conducted a research project that resulted in a Linked Data version of the NDC. A memorandum on research cooperation was signed by the NDL and the JLA on February 19, 2015.
The cooperative research project was concluded with the briefing session to report the outcome of the project (Japanese) in July 2016.

  • Term: April 2015 – March 2016
  • Object: NDC 8th Edition and NDC 9th Edition
  • Overview: The digital data of the NDC, named MRDF, is provided by the JLA. The NDL and the JLA will carry out research in order to find solutions for several issues that affect the creation of a Linked Data version of the NDC (NDC-LD). Additionally, the NDL and the JLA will explore practical methods for maintaining and providing the Linked Data as Open Data.

You can see the outcome of the project (Japanese).

Beta version of International Standard Identifier for Libraries and Related Organizations (ISIL) LOD

The International Standard Identifier for Libraries and Related Organizations (ISIL) is an identifier which can be allocated to libraries and relevant organizations, such as archives and museums. The NDL provides ISIL LOD of as part of its promotion of LOD.

Cooperation with open data events and activities


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4. References

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Contact for inquiries about NDL's Linked Open Data

Standardization Section, Digital Information Distribution Division,
Digital Information Department, National Diet Library
E-mail: standardizationat n d l dot g o dot j p

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