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A Multilingual Metadata Schema Registry Based on RDF Schema

Mitsuharu Nagamori, Thomas Bakery, Tetsuo SakaguchiShigeo Sugimoto, Koichi Tabata

University of Library and Information Science (ULIS)GMD German National Research Center for Information Technologyy

fnagamori, saka, sugimoto, tabatag@ulis.ac.jp, thomas.baker@gmd.dey

Abstract

This paper describes a multilingual metadataschema registry which has been developed at the Uni-versity of Library and Information Science in Tsukuba,Japan. The registry currently has reference transla-tions of Dublin Core Metadata Element Set written in22 languages, DC Qualifiers and the DCMI Type Vo-cabulary written in English and Japanese, along withdescriptive elements of the Nippon Cataloging Rules.The registry is realized using XML technologies; meta-data schemas are expressed in the RDF Schema lan-guage, the RDF description is handled by a Java servletusing XSLT stylesheet. This paper shows the functionsand the architecture of the registry.Keywords: Metadata Schema, Metadata Registry,RDF Schema, XSLT Stylesheet

1 Introduction

Metadata schema registries (or simply, metadataregistries) are widely recognized as an important toolnot only to share information about metadata schemasbut also to enhance reusability of metadata schemas. Itis also known that metadata registries have importantroles for metadata interoperability among communitiesspeaking different languages and over time.

The ULIS Open Metadata Registry is a metadataschema registry which stores and provides metadataschemas written in multiple languages. The ULISOpen Metadata Registry provides reference descrip-tions of the basic 15 elements of Dublin Core Meta-data Element Set (DCMES), Dublin Core qualifiers,and a controlled vocabulary for the Type element rec-ommended by the Dublin Core Metadata Initiative(DCMI). As of June 2001, the 15 elements are ex-pressed in 22 languages1 and the qualifiers are ex-

1Arabic, Chinese, Taiwanese, Czech, Dutch, English, Finnish,

pressed in English and Japanese. The registry alsoexperimentally provides descriptive elements of Nip-pon Cataloging Rules2.

The metadata schemas are given in the RDF Schemalanguage. XML technologies, such as XSLT andDOM, are used to realize the registry. Unicode (UTF8)is used to encode reference descriptions in multiplelanguages in the current version, while local characterencoding schemes have been used in our previous ver-sion. This paper briefly describes the technologies andfunctions of the ULIS Open Metadata Registry.

2 Background

Multilingual description of elements and qualifiersis recognized as an important issue for broader usageof Dublin Core in the global community on the Internet[1]. The ULIS multilingual metadata registry began asa prototype developed at AIT, Thailand by a researchteam led by Thomas Baker in 1998. The first ULISmultilingual registry was developed by the authors in1999 based on the prior system. In this system, refer-ence descriptions were encoded in RDF Schema lan-guage and the texts were encoded with local charactersets, such as EUC-JP for Japanese, Big5 for Chinese,TIS for Thai, and so forth. In this prior system, a multi-lingual text browsing technology named MHTML wasadopted to display multilingual texts on off-the-shelfWWW browsers. Since MHTML is an applet-basedtechnology to display texts on an applet without us-ing local fonts, users need no a-priori font loading todisplay multilingual texts on their Web browser[2]. Inthe latest MHTML-based registry, the characters inthe texts are encoded in the ISO-2022-JP-2 standard,which is a character encoding scheme for multiple lan-guages. Figure 1 shows a user interface to chooseelements and languages, and Figure 2 shows a set of

French, German, Greek, Indonesian, Italian, Japanese, Korean,Maori, Norwegian, Polish, Portuguese, Spanish, Swedish, Thai,

©2001 National Institute of Informatics

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Figure 1. A Interface to Choose Elements and Languages

Figure 2. Reference Descriptions of "Ti-tle" in Portuguese, English and Greek

texts displayed on a browser.

3 ULIS Metadata Schema Registry - Sys-tem Architecture and Examples

Figure 3 shows the overview of the system archi-tecture. The system is composed of three major com-ponents. These components are (1) metadata schema

Ukrainian2Anglo-American Cataloging Rules’ counterpart in Japan

MetadataSchema

DescriptionDatabase

Browse

Edit

Search

Registry Functions

User User User

User Interface

Multilingual Metadata Schema Registry

Figure 3. System Architecture of theMetadata Schema Registry

description database, (2) a servlet which provides reg-istry functions such as editing, browsing and search-ing, and (3) user interfaces defined in accordance withfunctions provided by the servlet.

Figure 4 shows English and Japanese reference de-scriptions of the Title element of DCMES encoded inthe RDF Schema language. Figure 5 shows a browserinterface which shows reference descriptions in Thai.Figures 6 and 7 show a search interface and search re-sult, respectively. A word "title" is given for search inFigure 6. A list of descriptions which include "title"in its definition are displayed in Figure 7. Figure 8shows an editing tool where metadata schema design-

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Figure 4. English and Japanese Refer-ence Descriptions of "Title" Element ofDCMES

Figure 5. Browsing Metadata Schema:Dublin Core in Thai

ers can edit a reference description of a vocabulary,i.e. elements, qualifiers and other terms. The editorconverts the text to/from RDF Schema description inthe database.

The registry system has a generic architecture shownin Figure 9. It has a servlet that has basic functionssuch as edit, browse and search, which are defined in-dependently of metadata schemas. Every HTML doc-ument that comprises the user interface of the registryis dynamically created from a user interface specifi-cation and a metadata schema description(s) using anXSLT stylesheet. The user interface specification isdefined based on a metadata schema, and all metadataschema descriptions are given in the RDF Schema lan-guage. Each XSLT stylesheet is defined based on itscorresponding registry function. Is is not necessary tomodify the servlet in order to add new schemas to theregistry. Thus, the registry is easily extended to realizenew user interface in accordance with new metadataschemas and new user interfaces.

Figure 6. Search for "title"

Figure 7. Search Result for "title"

4 Discussion and Future Extension

Metadata schema registries have been recognizedas important for the development and maintenance ofmetadata vocabularies. UKOLN has developed a reg-istry which has a crosswalk function [3]. One of theMax Planck Institutes has a German Metadata Registry[4]. The SCHEMAS Forum funded by the IST programof EU provides access to many metadata schemas [5].The registry of the SCHEMAS Forum is built on topof using an open source software toolkit for metadataregistries called EOR [6].

As of June 2001, the ULIS registry stores 27 en-tries in the schema database. The Search function isone of the crucial issues for the scalability of the reg-istry. EOR, for example, uses MySQL for this purpose.However, a text search technology which can han-dle RDF Schema descriptions in multiple languagesis needed. In this study, XPath is being used to real-ize the search function both because XPath is usefulfor realizing XML text string searching for multilin-gual texts encoded in UTF8 and because it is portable.Our next step is to use a database management soft-ware tool which accepts UTF8 as the basis for the datamanagement.

The authors discussed the versioning issue for

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Figure 8. Input Form for Creating NewSchema

Dublin Core in our previous paper[7]. The primaryrole of metadata registries is to serve as an authorita-tive provider of metadata schemas over the long term.In addition, metadata registries are expected to sup-port the development and customization of metadatavocabularies for various local- and/or domain-specificcommunities. Registries should provide software toolsor services to enhance the re-usability and interoper-ability of metadata schemas among communities andto help a community develop metadata-base servicesin accordance with their local requirements.

At ULIS, the authors are developing a subject gate-way for network resources which are useful for publiclibrary users and written in Asian languages. This is acollaborative activity with the Internet Public Library atUniversity of Michigan [8]. As of June 2001, Chinese,Korean and Japanese resources have been collected.It uses a metadata schema based on IMS and DublinCore. For the development of this subject gateway, wehave noticed that the XML-based technology shownin Figure 9 is applicable for developing software toolsto support the development of the service, and alsosubject gateways in general, even though there is afundamental difference between them; i.e., a registryhandles metadata schemas and a subject gateway doesmetadata instances. We are developing a support toolto create metadata-based application systems based onthe XML-based technology developed in this study.

5 Conclusion

For the development of metadata schemas in theglobal network environment, we have to cope withthe dilemma that we need globally approved metadatastandard for global interoperability of metadata and,on the other hand, local and/or domain specific com-munities need metadata schemas which are well-suitedto their requirements. The authors believe that meta-

schemadefinition

RDF Schema

XSLT Stylesheets

interfacedefinition

MetadataSchema

DescriptionDatabase

Registry Manager Servlet

User User User

WWW Browser

Browse Edit

Java Classes

Search

Apache Http Server

HTML

Figure 9. Registry Architecture

data schema registry is a key component in the networkenvironment to cope with this dilemma. In addition,long-term maintenance of metadata schemas,which in-clude traceability of version and translation history, isalso an important issue for metadata registries. Theseissues are left for further research.

acknowledgements: This research is supported byGrants-in-Aid for Scientific Research #13558039 inpart.

References

[1] Baker, T., Dublin Core in Multiple Languages:Esperanto, Interlingua, or Pidgin?, Proceedingsof the International Symposium on Research, De-velopment and Practice in Digital Libraries 1997,1997, pp. 8–15.

[2] Sugimoto, S. et al., Experimental Studies on anApplet-Based Document Viewer for MultilingualWWW Documents - Functional Extension of andLessons Learned from Multilingual HTML, Pro-ceedings of ECDL98 (LNCS 1513, Springer), pp199-214, 1998.10

[3] DESIRE Metadata Registry.http://desire.ukoln.ac.uk/registry/index.php3

[4] German Metadata Registry,http://www.mpib-berlin.mpg.de/dok/metadata/gmr/gmr1e.htm

[5] SCHEMAS: Forum for Metadata Schema De-signers and Implementers. http://www.schemas-forum.org/

[6] The EOR Toolkit. http://eor.dublincore.org/

[7] Sugimoto S., et al. Versioning the DublinCore across Multiple Languages and over TimeProceedings of SAINT 2001 workshop IEEEpp.151-156 2001.1

[8] Internet Public Library, http://www.ipl.org/