Proc. Intʼl Conf. on Dublin Core and Metadata Applications 2019Japan Search RDF Schema: a dual-layered approach to describe
items from heterogeneous data sources
Daichi Machiya
National Diet Library,Japand-machiy@ndl.go.jp

Tomoko Okuda
National Diet Library,Japan
standardization@ndl.go.jp

Masahide Kanzaki
Xenon Limited Partners,Japanmkanzaki@gmail.com

Abstract
The National Diet Library, Japan (NDL), with support by Xenon Limited Partners, has designed a
new metadata schema based on the RDF model while developing a national platform for metadata
aggregation and sharing, “Japan Search”. Japan Search collects metadata from libraries, museums,archives, and research institutions across the country, and provides an integrated search service aswell as APIs (SPARQL Endpoint and REST-API). The aim of this paper is to introduce the newschema, highlighting its dual-layered data model and the normalization of temporal (When), spatial(Where), and agential (Who) information provided in the source data.
Keywords: National Diet Library; national library; Japanese library; Linked Open Data; metadata
aggregation; metadata model; digital cultural heritage

1. Introduction
The NDL has been providing an integrated search service of the materials held by libraries,universities, archives, and museums through NDL Search since 2012. It receives, stores, andoutputs metadata based on a Dublin Core application profile, DC-NDL. Since 2015, the NDL has
been working closely with related parties including the Intellectual Property Strategy Promotion
Bureau in promoting digitization and online access of cultural and scholarly contents held byJapanese institutions. This led to the building of a new cross-sector integrated portal for culturaland scholarly contents. The new portal “Japan Search” made its debut on February 27, 2019.
Japan Search is not merely an integrated search service; it has also implemented several features
to motivate potential partner institutions. Among them is the RDF store, where the aggregatedmetadata are converted to a standard schema based RDF model. The new schema is called “JapanSearch RDF Schema”, or “JPS RDF” for short. The schema primarily uses schema.org vocabulary,which is convenient for a wide range of users and applications, along with some additional
properties defined at Japan Search.
As of April 2019, Japan Search presents RDF descriptions of 16,651,685 items with over 700
million statements.

2. JPS RDF Schema
2.1. Data ModelJPS RDF adopts a data model comprising of two parts: (1) content description with normalized
values, and (2) information on access to the content and on the source database from which
metadata is submitted to Japan Search. The content description subsequently consists of two layers:a simple description of the content using well-known schema.org properties and corresponding
structured descriptions using properties defined in the Japan Search system.
The rationale behind this data model is to enable users to effectively find content matching theirinterests across heterogeneous domains, while preserving metadata provenance andacknowledgement to the provider of the content. The dual-layered content description part achieves

21
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Proc. Intʼl Conf. on Dublin Core and Metadata Applications 2019the former through a combination of a simple triple pattern query and a complex refined search.
The access and source information invites the users to the provider of the content, and informs theusers whether the provider is a holder of the original object or a database publisher of the digitizedsurrogates. The source data submitted by partner institutions (hereinafter referred to as “sourcedata”) will be kept in a JSON format without modifying properties or values. It is then given a URI,and is linked from the description in JPS RDF, in order for users to access the original catalog
information.
For the simple description, schema.org properties were chosen after careful comparison with theterms in other major vocabularies such as DCMI Metadata Terms and BIBFRAME. The project
preferred the domain-independent nature and extensibility of the schema.org vocabulary. While thestructured description could be expressed in several ways, the project decided to introduce its own
vocabulary in order to make maximum use of this structure.
2.2. Simple schema.org descriptions and value normalization
When the source data of a certain piece of content is submitted to Japan Search, values thatrepresent time (When) and place (Where) are normalized, so that the data submitted by various
institutions can be retrieved in a unified form. In the JPS RDF, a year is the smallest unit of Time(i.e. temporal information), while the prefecture is the smallest unit for Place (i.e. spatialinformation). Names of people and organizations are also normalized by matching against a set ofnamed entity dictionaries prepared for the mapping systems. The normalized data are given an IRI(International Resource Identifier), and linked to LOD hubs, such as entity URIs in acknowledged
authority files, VIAF, and Wikidata (Fig. 1).

Fig. 1. Normalization of Name “喜多川歌麿 (Kitagawa, Utamaro）”

These normalized values of time, place, and name are described with schema.org properties;
e.g. schema:temporal, schema:spatial, and schema:contributor (or schema:creator), without distinguishing the relationship of the year, the place, or the name to thecontent. Any indication of time contained in the source data can be accommodated by the property
schema:temporal, whether it is the publication date of a book or the excavation date of an22
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Proc. Intʼl Conf. on Dublin Core and Metadata Applications 2019archeological artifact. Similarly, any indication of a place will be accommodated byschema:spatial, whether it is the place for collecting a specimen or the place illustrated in awoodblock print. This makes it easy for users to discover the content related to a particular place,
period of time, or creator/contributor by a simple triple pattern query.
Although those normalized IRIs have Japanese names as their local parts, they have English
labels as well. English-speaking users can take advantage of the normalized values via these labels(schema:name with language tag "en") or the above-mentioned LOD links (owl:sameAs) (Fig.
2).

Fig. 2. An example of a simple SPARQL query requesting the contents related to Mie prefecture

2.3. Structured description with JPS RDF properties
While simple description using schema.org properties allows casting a wide net, some may wanta refined search result using complex conditions. JPS RDF defines properties such asjps:spatial, jps:temporal, and jps:agential (jps: is the prefix for the namespace forthe properties defined at Japan Search) to express structured description. The structured description
complements the corresponding simple description with a property jps:relationType thatspecifies the relationship of the time/place/name to the content it is linked to. The structured
description contains the same value as the corresponding simple description in jps:value, which
designates the representative (normalized) value of this construct. By using the relationship typeassociated within the jps:spatial structured node, complex queries such as “ceramics createdin Mie Prefecture” (see the structure in Fig. 3) or “specimens collected in Kanagawa prefecture in
the 1930s” can be composed.

Fig. 3. Structured description of Place using jps:relationType

The structured property nodes preserve original values provided by the content provider, so thatdata consumers can obtain rich descriptions missed during normalization. By adding contextual
information, e.g. role (jps:relationType), and original values to the relation, the structured
properties of JPS RDF are meant to be a sort of "property graph" or annotation of properties. WhileRDF has no built-in mechanism to annotate a property, the JPS RDF’s dual-layered model makes
it possible to annotate the relation with detailed information while retaining a simple style ofproperty to facilitate easy and straightforward queries.

23This article is licensed under a Creative Commons Attribution 4.0 International License,
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Proc. Intʼl Conf. on Dublin Core and Metadata Applications 2019

2.4. Access Information and Source Information
Information on access to the content is provided in a structured form as an instance of the “AccessInformation” class, using the property jps:accessInfo. This includes both the access to theoriginal cultural artifact and to its digital surrogates. For example, in the case of a painting, a user
can visit the museum with information given by schema:provider and find the exhibited original
through its catalog number in jps:contentId, while obtaining its digitized image withschema:associatedMedia or through a landing page designated by schema:url. The accessinformation can also accommodate rights and license information.
The class “Source Information” describes structured information on the source data and its
provider. The value for schema:provider in the source information represents the databases thatsubmit data to Japan Search. The values of schema:url here provide the URLs of the web page
where the provider has published the source data in their own services. Source information also
provides the last date the source data was modified (schema:dateModified).

3. SPARQL Endpoint and Use Case Scenarios
The normalized metadata in the JPS RDF store can be retrieved via the Japan Search SPARQL
Endpoint (https://jpsearch.go.jp/rdf/sparql/). Since the normalized data in Japan Search are linked
to LOD URIs, it is possible to cross-walk Japan Search and other RDF data sources (e,g, Europeana,Wikidata, major national libraries) with SPARQL 1.1 Federated Query. Figure 4 shows the resultsof such a query, which uses a DBpedia URI to identify 曲亭馬琴 (Kyokutei, Bakin, 1767-1848),
then retrieves his works from Europeana and Japan Search. In this way, users can find works ofKyokutei Bakin in a single step: not only those held by Japanese institutions via Japan Search, butalso those held in European institutions via Europeana.

Fig. 4. Federated Query results for works by “曲亭⾺琴 (Kyokutei, Bakin)”, Europeana and Japan SearchExperiments on utilization of Japan Search have been attempted since its launch. Among suchattempts is a provisional analysis of the types of content that characterize each prefecture. The
result demonstrates that Tokyo is by far the largest holder of JPS content, with its sheer number ofproceedings, publications, and journal articles. The same analysis also reveals that architectural
heritage is rather more concentrated in the western part of Japan than in the east. The results ofanalysis can be effectively visualized using the normalized temporal and spatial data, which can beused to showcase what would be made visible by an aggregated mass of data. The project is aiming
to release a new function where online galleries of various content can be generated automatically
based on the links contained in JPS RDF.

24
This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format,
as long as you give appropriate credit to the original author(s) and cite the source.

https://doi.org/10.23106/dcmi.952141590

Proc. Intʼl Conf. on Dublin Core and Metadata Applications 2019

4. Conclusion
The JPS RDF is designed to serve a wide range of uses from simple to complex searches,federated query with outside RDF sources, and data analysis of cultural contents. The system andthe schema will be continually amended, with the year 2020 as a tentative cutoff date. In the comingyears, the NDL will further strengthen cooperation with cultural and scholarly institutions acrossJapan for the refinement and enrichment of the aggregated data and for the promotion of innovative
uses of cultural and scholarly content data.

References
National Diet Library. (2019). Japan Search (beta): For Developers. Retrieved April 25, 2019, fromhttps://jpsearch.go.jp/api.
Kanzaki, Masahide. (2019). Japan Search Unofficial Support Page. https://www.kanzaki.com/works/ld/jpsearch/.
Retrieved April 25, 2019 from https://www.kanzaki.com/works/ld/jpsearch/.

25
This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format,
as long as you give appropriate credit to the original author(s) and cite the source.

https://doi.org/10.23106/dcmi.952141590

Proc. Intʼl Conf. on Dublin Core and Metadata Applications 201921
This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format,
as long as you give appropriate credit to the original author(s) and cite the source.

https://doi.org/10.23106/dcmi.952141590