Resource Description Framework (RDF)

The Resource Description Framework (RDF) integrates a variety of applications from library catalogs and world-wide directories to syndication and aggregation of news, software, and content to personal collections of music, photos, and events using XML as an interchange syntax. The RDF specifications provide a lightweight ontology system to support the exchange of knowledge on the Web.

The W3C Semantic Web Activity Statement explains W3C's plans for RDF, including the RDF Core WG, Web Ontology and the RDF Interest Group.

RDF Specification Development

The RDF Specifications build on URI and XML technologies. The RDF suite of specifications consist of:

• RDF/XML Syntax Specification (Revised)
  W3C Recommendation
  Dave Beckett, ed.
• RDF Vocabulary Description Language 1.0: RDF Schema
  W3C Recomendation
  Dan Brickley, R.V. Guha, eds.
• RDF Primer
  W3C Recommendation
  Frank Manola, Eric Miller, eds.
• Resource Description Framework (RDF): Concepts and Abstract Syntax
  W3C Recommendation
  Graham Klyne, Jeremy Carroll, eds.
• RDF Semantics
  W3C Recommendation
  Patrick Hayes, ed.
• RDF Test Cases
  W3C Recommendation
  Jan Grant, Dave Beckett, eds.

These documents are intended to jointly replace the original Resource Description Framework specifications, RDF Model and Syntax (1999 Recommendation) and RDF Schema (1999 Proposed Recommendation).

RDF along with OWL are Semantic Web specifications.

Other relevant RDF W3C technical reports include:

• Composite Capability/Preference Profiles (CC/PP): Structure and Vocabularies 1.0
  W3C Recommendation 15 January 2004. Graham Klyne, Franklin Reynolds, Chris Woodrow, Hidetaka Ohto, Johan Hjelm, Mark H. Butler, Luu Tran
  CC/PP 1.0 is a system for expressing device capabilities and user preferences using RDF making it easier to deliver Web content to devices.
• Evaluation and Report Language (EARL) 1.0
  W3C Working Draft 06 December 2002. Wendy Chisholm, Sean B. Palmer
  EARL is a general-purpose language for expressing test results and defines a basic vocabulary in terms of RDF.
• An RDF Schema for P3P
  W3C Note 25 January 2002, Brian McBride, Rigo Wenning, Lorrie Cranor
• An RDF Schema for the XML Information Set
  W3C Note 06 April 2001, Richard Tobin
• Harvesting RDF Statements from XLinks
  W3C Note 29 September 2000, Ron Daniel Jr.
• Accessibility Features of SVG
  W3C Note 7 Aug 2000. Charles McCathieNevile, Marja-Riitta Koivunen discussion Sep 2000. implements an SVG-to-text convertor.
• PICS Rating Vocabularies in XML/RDF
  W3C NOTE 27 March 2000
• Cambridge Communiqué
  W3C NOTE Oct 1999 on application schema layering
• Web Architecture: Describing and Exchanging Data
  Berners-Lee, Connolly, Swick, W3C Note 7 June 1999
• Document Content Description for XML
  submitted July 1998 to the W3C by IBM and Microsoft. DCD is an RDF vocabulary to define document constraints in an XML syntax.
• W3C Data Formats
  W3C NOTE 29-October-1997, Tim Berners-Lee

See also Tim Berners-Lee's writings on Web Design Issues including Metadata Architecture and the OWL specifications which build on RDF and provide language for defining structured, Web-based ontologies which enable richer integration and interoperability of data among descriptive communities.

Bookmarks: Recommended Reading

These sites track developments related to RDF:

• Practical RDF by Shelly Powers
• Dave Beckett's Resource Description Framework (RDF) Resource Guide indexes RDF resources, including examples, documents, software, tools and projects that use it. since 1998.
• XMLhack site tracks RDF developments and discussion
• AgentWeb provides a resource guide and newsfeed covering Agent-related technologies
• SemanticWeb.org, coordinated by Stefan Decker, tracks RDF and Semantic Web related events and provides detailed background information on related technologies.
• The Eclectic weblog provides a summary of the (high traffic) XML-DEV mailing list. since Sep 1999

RDF Introductions and Overviews

While the RDF specs provide the most in-depth details about RDF, a number of shorter overviews and presentations are also available, for developers and for a general audience.

• RDF and Metadata, Tim Bray, June 09, 1998, xml.com
• Getting into RDF & Semantic Web using N3, Tim Berners-Lee
• Peer-to-Peer and the Semantic Web: The Power of Metadata, book chapter by Rael Dornfest & Dan Brickley
• An Idiot's Guide to the Resource Description Framework by Renato Iannella, January 25, 1999.
• RDF tutorial, Pierre-Antoine Champin (for developers)
• Summary of RDF API Discussions (for developers)
• Web Metadata: A Matter of Semantics by Ora Lassila, IEEE Internet Computing, July-August 1998
• An Introduction to the Resource Description Framework by Eric Miller, D-Lib Magazine, May 1998
• Putting RDF to Work, Edd Dumbill.
• Distributed XML: the role played by XML in the next-generation Web, Edd Dumbill.
• XML and the Web, by Tim Berners-Lee, XML World 2000, Boston 2000/09/06
• Frequently asked questions(FAQ) about RDF, with answers.

Articles and Presentations

• 2004-01, Weaving Meaning : An Overview of The Semantic Web, by Eric Miller. Presented at the University of Michigan, Ann Arbor, Michigan USA
• 2003-05, Semantic Web Tutorial Using N3 by Tim Berners-Lee, Dan Connolly, and Sandro Hawke at WWW2003.
• Weaving A Web of Ideas, Steven M. Cherry, IEEE Spectrum, September 2002
• The semantic web: How RDF will change learning technology standards, Mikael Nilsson, Center for User-Oriented IT-design, Royal Institute of Technology, Stockholm The semantic web: How RDF will change learning technology standards Mikael Nilsson, Center for User-Oriented IT-design, Royal Institute of Technology, Stockholm September 27, 2001
• Building a Semantic Web Site, Eric van der Vlist, XML.com, May 02, 2001
• DAML could take search to a new level, Jim Rapoza, PC Week Labs February 7, 2000
• A New Dawn, Glyn Moody, New Scientist, May 30, 1998
• Getting Deep Into Metadata, Nate Zelnick, The XML Files, a WebDeveloper.com Feature, June 12, 1998
• New Specs Are In the Works for Web Data, Brian Hannon, PC Week, May 29, 1998

See also Semantic Web presentations, W3C in The Press and Resource Description Framework Press in the RDF Resource Guide

Projects and Applications

RDF is an enabling technology for a wide variety of projects. The following is a sample; the Resource Description Framework Applications and Projects section in the RDF Resource Guide lists many more.

Content Authoring, Resource Description, and General Purpose Coperative Catalogs

• Adobe's XMP

  Adobe's Extensible Metadata Platform (XMP) is a labeling technology that allows you to embed data about a file, known as metadata, into the file itself. With XMP, desktop applications and back-end publishing systems gain a common method for capturing, sharing, and leveraging this valuable metadata Adobe.

• Creative Commons

  Creative Commons is devoted to expanding the range of creative work available for others to build upon and share.

• The FOAF Project

  Friend of a Friend (FOAF) project is about creating a Web of machine-readable homepages describing people, the links between them and the things they create and do.

  There are many different clients for navigating such machine-readable descriptions, foafnaut is one of these.

• Dublin Core Metadata Initiative

  The Dublin Core Metadata Initiative is an open forum engaged in the development of interoperable online metadata standards that support a broad range of purposes and business models. DCMI's activities include consensus-driven working groups, global workshops, conferences, standards liaison, and educational efforts to promote widespread acceptance of metadata standards and practices.

• OCLC Connexion

  (formally CORC - Cooperative Online Resource Catalog. CORC became a production service in July 2000; it started as a research project exploring the cooperative creation and sharing of metadata by libraries.

• Open Directory Project

  The Open Directory Project is the largest, most comprehensive human-edited directory of the Web. It is constructed and maintained by a vast, global community of volunteer editors.

  RDF dumps of the are available. Note, these dumps don't quite conform to the final RDF specification but rather to an earlier working draft. See Scripts to clean dmoz RDF output by Sergey Melnik, Digital Libraries Project, Database Group, Stanford University, USA, 20 March 2000.

• xmlTree

  xmlTree is an index of XML content providers. The index is served in both RDF form and presented for human readability.

• DSpace

  a newly developed digital repository created to capture, distribute and preserve the intellectual output of MIT.

  Leveraging and expending DSpace, the SIMILE project is using RDF and OWL to enhance inter-operability among digital assets, schemas, metadata, and services that are distributed across individual, community, and institutional stores. SIMILE is a joint project conducted by the W3C's Smantic Web Advanced Development group HP, MIT Libraries, and MIT's CSAIL.

• TAP

  TAP's goals are to enable the Semantic Web by providing some simple tools that make the web a giant distributed Database. TAP is open source development effort by R.V. Guha (IBM) and Rob McCool (Stanford) which provide a set of protocols and conventions that create a coherent whole of independantly produced bits of information, and a simple API to navigate the graph. Local, independantly managed knowledge bases can be aggegated to form selected centers of knowledge useful for particular applications.

• eventSherpa by SemaView.

  RDF based desktop application that allows one to find, organize, publish and consume calendar events. Semantic Web Events is a simple example of such a collaborate space.

Syndication, Aggregation, and Rating

While content rating was the application that originally motivated the developoment of PICS and RDF, syndication and aggregation have emerged as cost-effective applications of RDF.

• RDF Site Summary (RSS) 1.0

  lightweight multipurpose extensible metadata description and syndication format. proposed Aug 2000 to the RDF Interest Group

• XMLNews-Meta - A suite of specifications for exchanging news and information using open Web standards
• PRISM: Publishing Requirements for Industry Standard Metadata

  PRISM is a packaging and metadata format, similar to NewsML, RSS, and XMLNews-Meta. Like RSS 1.0 and XMLNews-Meta (but not NewsML), PRISM is based on RDF. PRISM is developed by an industry consortium of publishing software developers and publishers, including (among many others) Adobe, Quark, Condé Nast, and Time Inc.

• The UK Mirror Service is a national UK service providing mirrors/collections of software and data from around the world. It uses RDF internally for mirror description and mirror content description of over 4 million resources. April 2000
• Daniel Veillard's Linux Packages Database, a tool that makes use of RDF encoded metadata for locating and identifying dependencies between software packages available for the Linux operating system.
• Java, RDF, and the "Virtual Web", Leon Shklar (see also parts two and three), a Gamelan Tech Focus series on content syndication and aggregation strategies, September/October 1999.

Personal Collections: Music, Photos, Calendars, and Contacts

Some of the most exciting applications of RDF are at a smaller scale, very close to home. These applications depend on emerging technical and social mechanisms for managing trust on the web (access control, privacy, rights management), so as of this writing (Aug 2001) they tend to be advanced development projects more than production systems.

• MusicBrains Metadata Initiative

  Designed to create a portable and flexible means of storing and exchanging metadata related to digital audio and video tracks based on RDF/XML and Dublin Core

  • Aug presentation at RDF Core
• RDFPic, a tool to embed an RDF description of an image (digitized photograph) into the image itself. This tool implements the work described in Describing and retrieving photos using RDF and HTTP.
• Representing vCard v3.0 in RDF by Renato Iannella, Jan 1999

Developer Resources

A good introduction for developers is What is RDF? by Tim Bray on XML.com who have a growing series of articles and reports about RDF applications including Putting RDF to Work, RDF Calendar taskforce, RDF with prolog, RDF - why we should care - and RSS, Building the Semantic Web, The Semantic Web: A Primer and many others.

Developer news

• For comprehensive RDF information, try Dave Beckett's Resource Description Framework (RDF) Resource Guide especially the Editors and Tools and Appliations sections. ( RSS 1.0 news feed).
• XMLhack RDF developer news provides updates of developer announcements (RSS 1.0 news feed)

Java Developers

• The Jena Java RDF API and toolkit is a comprehensive Java system by Brian McBride, Jeremy Carroll, Andy Seaborne, Dave Reynolds and Ian Dickinson, HP Labs, Bristol. Jena contains an API for manipulating RDF models including statement and resource-centric methods using cascading calls for easy object orientated use, container support, the ARP RDF/XML parser, an RDF/XML writer, the RDQL query language, DAML support, persistent storage. Available under an open source, BSD-like license. See the jena discussion list for more information.
• The ICS-FORTH RDFSuite which are designed to provide open source, high-level scalable tools for the Semantic Web. This suite includes VAalidating RDF Parser (VRP), a RDF Schema Specific DataBase (RSSDB) and supporting RDF Query Language (RQL)
• Sesame is a Java-based storage and querying middleware system for RDF and RDF Schema, developed by Aidministrator Nederland bv. It contains an API for RDF(S) manipulations on repositories, an RDF Model Theory inference engine, and support for the RQL and RDQL query languages. Available as open source under the LGPL license
• IsaViz: A visual authoring tool for browsing and authoring RDF models represented as graphs. Developed by Emmanuel Pietriga of W3C and Xerox Research Centre Europe, IsaViz is based on the Zoomable Visual Transformation Machine.
• The Kowari Metastore^TM is an Open Source, massively scalable, transaction-safe, purpose-built database for the storage and retrieval of RDF. Kowari is licensed under the Mozilla Public License (MPL) v1.1.

  The Tucana Knowledge Store^TM (TKS) is a commercial RDF database managment system based on Kowari. TKS adds important features to Kowari, such as enterprise management and security, the ability to perform federated RDF queries over distributed servers and greater support for the Web Ontology Language (OWL).

Perl Developers

• The RDFStore Perl RDF API by Alberto Reggiori is a system for managing RDF models in Perl and includes a Perl version of the Stanford Java RDF API, the RDQL query language and persistent storage. See also the demo and work on proposed perl rdf api. Available under the same license as Perl via CPAN.

Python Developers

• W3C's Metalog Project: Metalog is a next-generation reasoning system for the Semantic Web, which has been designed to be particularly user-friendly and easy to use, so to showcase the initial potential of the Semantic Web. It is entirely written in Python, and can be easily interfaced with every logic programming system. Available under W3C open source license.
• The Redfoot RDF framework by James Tauber and Dan Krech provides a system for building distributed data-driven web applications with RDF and Python. It includes an RDF database, query API, template language, module architecture, editor all with web interface, sample applications and the beginnings of P2P support. Available under a BSD-style License.
• The W3C Semantic Web Area for Play by Tim Berners-Lee and Dan Connolly contains lots of small Python tools for RDF and beyond-RDF research tools including the Closed World Machine (CWM) data manipulator, rules processor and query system mostly using using the Notation 3 textual RDF syntax. Available under W3C open source license.
• The 4Suite 4RDF Python library provides open source tools for manipulating and querying RDF data, including inference capabilities. The xml.com article, 4RDF: A Library for Web Metadata includes an overview of the system with worked examples.

C developers

• The Redland RDF Application Framework library by Dave Beckett, Institute for Learning and Research Technology, University of Bristol is a portable C library that provides a high-level, object based interface for RDF allowing the model to be stored persistently, queried and manipulated. Includes the Raptor RDF Parser Toolkit for handling RDF/XML and other syntaxes and also provides Perl, Python, Tcl and Java interfaces. Available under open source / free software licenses (LGPL, GPL, MPL).
• RDFDB is a database that supports the RDF data model directly. It can load data from files or data can be inserted using the database API. It also supports an SQL-like query language. RDFDB is a very scalable and very fast triple store by R.V. Guha

C#

• Drive, by Rahul Singh. Drive is an RDF parser written in C# for the .NET platform. Its fully compliant with the W3C RDF syntax specification and is available as open source under the terms of the GNU LGPL license.
• EulerSharp, by Jos DeRoo. EulerSharp is an inference engine supporting logic based proofs. It is a backward-chaining reasoner enhanced with Euler path detection and will tell you whether a given set of facts and rules supports a given conclusion.

Tcl/Tk developers

• The XWMF - An eXtensible Web Modeling Framework project by Alexander Block and Reinhold Klapsing contains various tools in Tcl or XOTcl including a parser, data model query tool and graphical editor. Available under open source and/or LGPL licenses.

PHP developers

• RAP RDF API for PHP by Chris Bizer. A pure PHP package for manipulating RDF models and parsing/serializing the RDF/XML syntax. See also the documentation and online demo. GPL License. Version 0.3 with new rdf:nodeID and rdf:datatype support announced 13 January 2003.

LISP developers

• Wilbur. Wilbur is a lisp based toolkit for Semantic Web Programming.

  Wilbur is Nokia Research Center's toolkit for programming Semantic Web applications that use RDF (as well as XML and/or DAML+OIL), written in Common Lisp. It was developed by the Agent Technology group of Nokia Research Center. The work was supported in part by Nokia Mobile Phones (NMP) and Nokia Ventures Organization (NVO), as well as Nokia Venture Partners, LP. Wilbur is part of Nokia's Semantic Web activity.

Schemas

RDF is a general-purpose language for representing information in the Web. RDF Schema is a standard which describes how to use RDF to describe RDF vocabularies on the Web. The following are a just a sample of a few services that are available to see how people are creating and using these vocabularies.

• SchemaWeb provides a comprehensive directory of RDF schemas to be browsed and searched by human agents and also an extensive set of web services to be used by RDF agents and reasoning software applications that wish to obtain real-time schema information whilst processing RDF data.
• Dublin Core Metadata Registry is an RDF based metadata registry designed to provide users and applications an authoritative source of information about the Dublin Core element set and related vocabularies.
• DAML Ontology Library which organizes hundreds of ontologies in a variety of different ways (keyword, organization, submission date, etc.)

Related Technolologies

Conceptual Graphs

• Corese : A COnceptual REsource Search Engine The Corese platform implements an RDF/RDFS processor based on Conceptual Graphs (CG). Corese enables the processing of RDF Schemas and RDF statements within the CG formalism. The graph matching algorithm, called projection, enables to retrieve RDF statements according to a query and hence implements a search engine. Corese is a result of the Acacia project, Olivier Corby, INRIA.
• Conceptual Graphs and the Semantic Web, Tim Berners-Lee

SOAP/WSDL

• Using RDF with SOAP This article examines ways that SOAP can be used to communicate information in RDF models. It discusses ways of translating the fundamental data in RDF models to the SOAP encoding for PC-like exchange, or for directly passing parts of the model in RDF/XML serialized form.
• Basic XML and RDF techniques for knowledge management: part 1 Generate RDF using XSLT
• Basic XML and RDF techniques for knowledge management: part 2 Combining files into an RDF model, and basic RDF querying
• Supercharging WSDL with RDF This article focuses on building a bridge between the two specifications. It provides an example of what a Web service description might look like as an RDF file. It then goes on to discuss how to take advantage of an RDF visualization tool to generate a graph of the WSDL data. Finally, it presents a portion of a possible RDF Schema for WSDL.
• An initial RDF model for WSDL by Eric Prud'hommeaux

UML/MOF/XMI

• Representing UML in RDF The goal of this work is to make UML "RDF-compatible". This allows mixing and extending UML models and the language elements of UML itself on the Web in an open manner. A testbed converter that supports automatic translation from UML/XMI to RDFS/RDF/XML.
• A Layered Approach to Information Modeling and Interoperability on the Web Sergey Melnik, Stefan Decker, Database Group, Stanford University, : Sep 4, 2000
• A Discussion of the Relationship Between RDF-Schema and UML, Walter W. Chang, Advanced Technology Group, Adobe Systems, W3C Note, 04-Aug-1998
• Networked Knowledge Representation and Exchange using UML and RDF Stephen Cranefield, Journal of Digital Information, volume 1 issue 8, 2001-02-15
• DAML/UML Based Ontology Set from Lockheed Martin

TopicMaps

• XML Topic Maps through RDF Glasses, Presented at KT2001, Nikita Ogievetsky, Cogitech, Inc.
• DAML and Quantum Topic Maps, Presented at KT2002, Nikita Ogievetsky, Cogitech, Inc.
• XTM to RDF converter, Cogitech, Inc.
• Representing XML Topic Maps as RDF, Eric van der Vlist.
• RDF and Topic Maps: An Exercise in Convergence, Graham Moore.
• On the integration of Topic Maps and RDF, Martin Lacher.
• Topic maps, RDF, DAML, OIL. A comparison, Lars Marius Garshol.

Timeline: Historical Events and Publications

Events and publications in the history of RDF include...

• May 2001: WWW10 W3C's Semantic Web Track and the Semantic Web Developers Day. Hong Kong
• Feb 2001: RDF Interest Group meeting (26-27 Feb 2001)
• Feb 2001: Semantic Web Activity launched
• Oct 1999: "Cambridge Communiqué" W3C NOTE issued on application schema layering
• Sep 2000 XML World 2000 talk: XML and the Web, by Tim Berners-Lee.
• Mar 2000: RDF Schema Specification 1.0 published as a W3C Candidate Recommendation ( call for implementation)
• Aug 1999: RDF Interest Group created
• Feb 1999: RDF Model and Syntax Specification released as a W3C Recommendation (press release)
• May 1998 RDF - Using XML to describe Data, Swick, WWW8 presentation
• April 1998 WWW7 Tutorial, Using Web Metadata: Dublin Core and the Resource Description Framework, Lagoze, Miller, Lassila, Swick, Iannella, Schloss, Weibel
• Dec 1997 W3C Metadata Activity Statement presented to the W3C Membership
• Nov 1997 Introduction to RDF Metadata, W3C NOTE 1997-11-13, Ora Lassila
• Oct 1997 first RDF working draft released