The World Wide Web Consortium has announced "final approval of two key Semantic Web technologies, the revised Resource Description Framework (RDF) and the Web Ontology Language (OWL). RDF and OWL are Semantic Web standards that provide a framework for asset management, enterprise integration and the sharing and reuse of data on the Web. These standard formats for data sharing span application, enterprise, and community boundaries, since different types of users can share the same information even if they don't share the same software."

The Resource Description Framework (RDF) is a "language for representing information about resources in the World Wide Web. It is particularly intended for representing metadata about Web resources, such as the title, author, and modification date of a Web page, copyright and licensing information about a Web document, or the availability schedule for some shared resource. However, by generalizing the concept of a 'Web resource', RDF can also be used to represent information about things that can be identified on the Web, even when they cannot be directly retrieved on the Web. Examples include information about items available from on-line shopping facilities (e.g., information about specifications, prices, and availability), or the description of a Web user's preferences for information delivery." The W3C RDF Recommendation is presented six parts: Primer, Concepts, Syntax, Semantics, Vocabulary, and Test Cases.

The OWL Web Ontology Language is "intended to be used when the information contained in documents needs to be processed by applications, as opposed to situations where the content only needs to be presented to humans. OWL can be used to explicitly represent the meaning of terms in vocabularies and the relationships between those terms. This representation of terms and their interrelationships is called an ontology. OWL has more facilities for expressing meaning and semantics than XML, RDF, and RDF-S, and thus OWL goes beyond these languages in its ability to represent machine interpretable content on the Web. OWL is a revision of the DAML+OIL web ontology language incorporating lessons learned from the design and application of DAML+OIL." W3C has published the OWL Recommendation in six documents: Use Cases, Overview, Guide, Language Reference, Test Cases, and Language Semantics and Abstract Syntax.

RDF Bibliographic Information and Summary

• RDF Primer. W3C Recommendation 10-February-2004. Edited by Frank Manola and Eric Miller (W3C). Series Editor: Brian McBride (Hewlett-Packard Laboratories). Version URL: http://www.w3.org/TR/2004/REC-rdf-primer-20040210/. Latest version URL: http://www.w3.org/TR/rdf-primer/ Previous version URL: http://www.w3.org/TR/2003/PR-rdf-primer-20031215/.

  Abstract: "The Resource Description Framework (RDF) is a language for representing information about resources in the World Wide Web. This Primer is designed to provide the reader with the basic knowledge required to effectively use RDF. It introduces the basic concepts of RDF and describes its XML syntax. It describes how to define RDF vocabularies using the RDF Vocabulary Description Language, and gives an overview of some deployed RDF applications. It also describes the content and purpose of other RDF specification documents."

• Resource Description Framework (RDF): Concepts and Abstract Syntax. W3C Recommendation 10-February-2004. Edited by Graham Klyne (Nine by Nine), and Jeremy J. Carroll (Hewlett Packard Labs). Series Editor: Brian McBride (Hewlett-Packard Laboratories). Version URL: http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/. Latest version URL: http://www.w3.org/TR/rdf-concepts/. Previous version URL: http://www.w3.org/TR/2003/PR-rdf-concepts-20031215/.

  The Resource Description Framework (RDF) is a framework for representing information in the Web. RDF Concepts and Abstract Syntax defines an abstract syntax on which RDF is based, and which serves to link its concrete syntax to its formal semantics. It also includes discussion of design goals, key concepts, datatyping, character normalization and handling of URI references.

• RDF/XML Syntax Specification (Revised). W3C Recommendation 10-February-2004. Edited by Dave Beckett (University of Bristol). Series Editor: Brian McBride (Hewlett-Packard Laboratories). Version URL: http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/. Latest version URL: http://www.w3.org/TR/rdf-syntax-grammar/. Previous version URL: http://www.w3.org/TR/2003/PR-rdf-syntax-grammar-20031215/.

  The Resource Description Framework (RDF) is a general-purpose language for representing information in the Web. This document defines an XML syntax for RDF called RDF/XML in terms of Namespaces in XML, the XML Information Set and XML Base. The formal grammar for the syntax is annotated with actions generating triples of the RDF graph as defined in RDF Concepts and Abstract Syntax. The triples are written using the N-Triples RDF graph serializing format which enables more precise recording of the mapping in a machine processable form. The mappings are recorded as tests cases, gathered and published in RDF Test Cases.

• RDF Vocabulary Description Language 1.0: RDF Schema. W3C Recommendation 10-February-2004. Edited by Dan Brickley (W3C) and R.V. Guha (IBM). Version URL: http://www.w3.org/TR/2004/REC-rdf-schema-20040210/. Latest version URL: . Previous version URL: http://www.w3.org/TR/2003/PR-rdf-schema-20031215/.

  The Resource Description Framework (RDF) is a general-purpose language for representing information in the Web. This specification describes how to use RDF to describe RDF vocabularies. This specification defines a vocabulary for this purpose and defines other built-in RDF vocabulary initially specified in the RDF Model and Syntax Specification. This specification introduces RDF's vocabulary description language, RDF Schema. It is complemented by several companion documents which describe RDF's XML encoding, mathematical foundations, and Resource Description Framework (RDF): Concepts and Abstract Syntax. The RDF Primer provides an informal introduction and examples of the use of the concepts specified in this document. This document is intended to provide a clear specification of the RDF vocabulary description language to those who find the formal semantics specification, RDF Semantics daunting. Thus, this document duplicates material also specified in the RDF Semantics specification . Where there is disagreement between this document and the RDF Semantics specification, the RDF Semantics specification should be taken to be correct...

  RDF properties may be thought of as attributes of resources and in this sense correspond to traditional attribute-value pairs. RDF properties also represent relationships between resources. RDF however, provides no mechanisms for describing these properties, nor does it provide any mechanisms for describing the relationships between these properties and other resources. That is the role of the RDF vocabulary description language, RDF Schema. RDF Schema defines classes and properties that may be used to describe classes, properties and other resources. This document does not specify a vocabulary of descriptive properties such as "author". Instead it specifies mechanisms that may be used to name and describe properties and the classes of resource they describe. RDF's vocabulary description language, RDF Schema, is a semantic extension of RDF. It provides mechanisms for describing groups of related resources and the relationships between these resources. RDF Schema vocabulary descriptions are written in RDF using the terms described in this document. These resources are used to determine characteristics of other resources, such as the domains and ranges of properties...

• RDF Semantics. W3C Recommendation 10-February-2004. Edited by Patrick Hayes (IHMC). Series Editor: Brian McBride (Hewlett-Packard Laboratories). Version URL: http://www.w3.org/TR/2004/REC-rdf-mt-20040210/. Latest version URL: http://www.w3.org/TR/rdf-mt/. Previous version URL: http://www.w3.org/TR/2003/PR-rdf-mt-20031215/.

  This is a specification of a precise semantics, and corresponding complete systems of inference rules, for the Resource Description Framework (RDF) and RDF Schema (RDFS)... This document uses a basic technique called model theory for specifying the semantics of a formal language... Model theory assumes that the language refers to a 'world', and describes the minimal conditions that a world must satisfy in order to assign an appropriate meaning for every expression in the language. A particular world is called an interpretation, so that model theory might be better called 'interpretation theory'. The idea is to provide an abstract, mathematical account of the properties that any such interpretation must have, making as few assumptions as possible about its actual nature or intrinsic structure, thereby retaining as much generality as possible. The chief utility of a formal semantic theory is not to provide any deep analysis of the nature of the things being described by the language or to suggest any particular processing model, but rather to provide a technical way to determine when inference processes are valid, i.e., when they preserve truth. This provides the maximal freedom for implementations while preserving a globally coherent notion of meaning... Model theory tries to be metaphysically and ontologically neutral. It is typically couched in the language of set theory simply because that is the normal language of mathematics - for example, this semantics assumes that names denote things in a set IR called the 'universe' - but the use of set-theoretic language here is not supposed to imply that the things in the universe are set-theoretic in nature. Model theory is usually most relevant to implementation via the notion of entailment, described later, which makes it possible to define valid inference rules..."

• RDF Test Cases. W3C Recommendation 10-February-2004. Edited by Jan Grant (ILRT, University of Bristol) and Dave Beckett (ILRT, University of Bristol). Series Editor: Brian McBride (Hewlett-Packard Laboratories). Version URL: http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/. Latest version URL: http://www.w3.org/TR/rdf-testcases/. Previous version URL: http://www.w3.org/TR/2003/PR-rdf-testcases-20031215/.

  "This document describes the RDF Test Cases deliverable for the RDF Core Working Group as defined in the Working Group's Charter. One of the deliverables specified in Charter of the RDF Core Working Group is: 'a set of machine-processable test cases corresponding to technical issues addressed by the Working Group'. This document describes the test cases that fulfill that deliverable but it does not contain the test cases themselves. The test cases are available at http://www.w3.org/2000/10/rdf-tests/rdfcore/..."

OWL Bibliographic Information and Summary

• OWL Web Ontology Language Use Cases and Requirements. W3C Recommendation 10-February-2004. Edited by Jeff Heflin (Lehigh University). Version URL: http://www.w3.org/TR/2004/REC-webont-req-20040210/. Latest version URL: http://www.w3.org/TR/webont-req/. Previous version URL: http://www.w3.org/TR/2003/PR-webont-req-20031215/.

  This document specifies usage scenarios, goals and requirements for a web ontology language. An ontology formally defines a common set of terms that are used to describe and represent a domain. Ontologies can be used by automated tools to power advanced services such as more accurate web search, intelligent software agents and knowledge management.

• OWL Web Ontology Language Overview. W3C Recommendation 10-February-2004. Edited by Deborah L. McGuinness (Knowledge Systems Laboratory, Stanford University) and Frank van Harmelen (Vrije Universiteit, Amsterdam). Version URL: http://www.w3.org/TR/2004/REC-owl-features-20040210/. Latest version URL: http://www.w3.org/TR/owl-features/. Previous version URL: http://www.w3.org/TR/2003/PR-owl-features-20031215/.

  The OWL Web Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans. OWL facilitates greater machine interpretability of Web content than that supported by XML, RDF, and RDF Schema (RDF-S) by providing additional vocabulary along with a formal semantics. OWL has three increasingly-expressive sublanguages: OWL Lite, OWL DL, and OWL Full.

  This document is written for readers who want a first impression of the capabilities of OWL. It provides an introduction to OWL by informally describing the features of each of the sublanguages of OWL. Some knowledge of RDF Schema is useful for understanding this document, but not essential. After this document, interested readers may turn to the OWL Guide for more detailed descriptions and extensive examples on the features of OWL. The normative formal definition of OWL can be found in the OWL Semantics and Abstract Syntax.

• OWL Web Ontology Language Guide. W3C Recommendation 10-February-2004. Edited by Michael K. Smith (Electronic Data Systems), Chris Welty (IBM Research), and Deborah L. McGuinness (Knowledge Systems Laboratory, Stanford University). Version URL: http://www.w3.org/TR/2004/REC-owl-guide-20040210/. Latest version URL: http://www.w3.org/TR/owl-guide/. Previous version URL: http://www.w3.org/TR/2003/PR-owl-guide-20031215/.

  "The World Wide Web as it is currently constituted resembles a poorly mapped geography. Our insight into the documents and capabilities available are based on keyword searches, abetted by clever use of document connectivity and usage patterns. The sheer mass of this data is unmanageable without powerful tool support. In order to map this terrain more precisely, computational agents require machine-readable descriptions of the content and capabilities of Web accessible resources. These descriptions must be in addition to the human-readable versions of that information. The OWL Web Ontology Language is intended to provide a language that can be used to describe the classes and relations between them that are inherent in Web documents and applications. This document demonstrates the use of the OWL language to: (1) formalize a domain by defining classes and properties of those classes; (2) define individuals and assert properties about them, and (3) reason about these classes and individuals to the degree permitted by the formal semantics of the OWL language. The sections are organized to present an incremental definition of a set of classes, properties and individuals, beginning with the fundamentals and proceeding to more complex language components..."

• OWL Web Ontology Language Reference. W3C Recommendation 10-February-2004. Produced by the W3C Web Ontology Working Group. Edited by Mike Dean (BBN Technologies) and Guus Schreiber (Free University Amsterdam). Authors: Sean Bechhofer (University of Manchester), Frank van Harmelen (Free University Amsterdam), Jim Hendler (University of Maryland), Ian Horrocks (University of Manchester), Deborah L. McGuinness (Stanford University), Peter F. Patel-Schneider (Bell Labs Research, Lucent Technologies), and Lynn Andrea Stein (Franklin W. Olin College of Engineering). Version URL: http://www.w3.org/TR/2004/REC-owl-ref-20040210/. Latest version URL: http://www.w3.org/TR/owl-ref/. Previous version URL: http://www.w3.org/TR/2003/PR-owl-ref-20031215/.

  The Web Ontology Language OWL is a semantic markup language for publishing and sharing ontologies on the World Wide Web. OWL is developed as a vocabulary extension of RDF (the Resource Description Framework) and is derived from the DAML+OIL Web Ontology Language. This document contains a structured informal description of the full set of OWL language constructs and is meant to serve as a reference for OWL users who want to construct OWL ontologies... An OWL ontology is an RDF graph [RDF Concepts], which is in turn a set of RDF triples. As with any RDF graph, an OWL ontology graph can be written in many different syntactic forms (as described in the RDF/XML Syntax Specification (Revised). The current document uses some specific syntactic forms of RDF/XML for representing triples (as does the Guide document) . However, the meaning of an OWL ontology is solely determined by the RDF graph. Thus, it is allowable to use other syntactic RDF/XML forms, as long as these result in the same underlying set of RDF triples. Such other syntactic forms would then carry exactly the same meaning as the syntactic form used in this document... OWL is a vocabulary extension of RDF. Thus any RDF graph forms an OWL Full ontology. Further, the meaning given to an RDF graph by OWL includes the meaning given to the graph by RDF. OWL Full ontologies can thus include arbitrary RDF content, which is treated in a manner consistent with its treatment by RDF. OWL assigns an additional meaning to certain RDF triples. The OWL Semantics and Abstract Syntax document specifies exactly which triples are assigned a specific meaning, and what this meaning is..."

• OWL Web Ontology Language Test Cases. W3C Recommendation 10-February-2004. See also "A Test Repository for the W3C Web Ontology Working Group." Edited by Jeremy J. Carroll (HP) and Jos De Roo (AGFA) Version URL: http://www.w3.org/TR/2004/REC-owl-test-20040210/. Latest version URL: http://www.w3.org/TR/owl-test/. Previous version URL: http://www.w3.org/TR/2003/PR-owl-test-20031215/.

  This document contains and presents test cases for the Web Ontology Language (OWL) approved by the Web Ontology Working Group. Many of the test cases illustrate the correct usage of the Web Ontology Language (OWL), and the formal meaning of its constructs. Other test cases illustrate the resolution of issues considered by the Working Group. Conformance for OWL documents and OWL document checkers is specified.

• OWL Web Ontology Language Semantics and Abstract Syntax. W3C Recommendation 10-February-2004. Edited by Peter F. Patel-Schneider (Bell Labs Research, Lucent Technologies), Patrick Hayes (IHMC, University of West Florida), and Ian Horrocks (University of Manchester). Version URL: http://www.w3.org/TR/2004/REC-owl-semantics-20040210/. Latest version URL: http://www.w3.org/TR/owl-semantics/. Previous version URL: http://www.w3.org/TR/2003/PR-owl-semantics-20031215/.

  "This description of OWL, the Web Ontology Language being designed by the W3C Web Ontology Working Group, contains a high-level abstract syntax for both OWL DL and OWL Lite, sublanguages of OWL. A model-theoretic semantics is given to provide a formal meaning for OWL ontologies written in this abstract syntax. A model-theoretic semantics in the form of an extension to the RDF semantics is also given to provide a formal meaning for OWL ontologies as RDF graphs (OWL Full). A mapping from the abstract syntax to RDF graphs is given and the two model theories are shown to have the same consequences on OWL ontologies that can be written in the abstract syntax."

From the W3C Announcement

World Wide Web Consortium Issues RDF and OWL Recommendations

Today's announcement [from W3C] marks the emergence of the Semantic Web as a broad-based, commercial-grade platform for data on the Web. The deployment of these standards in commercial products and services signals the transition of Semantic Web technology from what was largely a research and advanced development project over the last five years, to more practical technology deployed in mass market tools that enables more flexible access to structured data on the Web. Testimonials from enterprise-scale implementors and independent developers illustrate current uses of these standards on the Web today.

"RDF and OWL make a strong foundation for Semantic Web applications," said Tim Berners-Lee, W3C Director and inventor of the World Wide Web. "Their approval as W3C Recommendations come at a time when new products spring up in areas as diverse as Enterprise Integration and medical decision support. It's not unlike the early days of the Web, when once people saw how it worked, they understood its power. We're entering that phase now, where people can see the beginnings of the Semantic Web at work."

A World Wide Web Consortium (W3C) Recommendation is understood by industry and the Web community at large as a Web standard. Each Recommendation is a stable specification developed by a W3C Working Group and reviewed by the W3C Membership. Recommendations promote interoperability of Web technologies of the Web by explicitly conveying the industry consensus formed by the Working Group.

Wide Range of Applications Growing from New Semantic Web Standards

Semantic Web-enabled software using RDF and OWL include:

• Content creation applications: Authors can connect metadata (subject, creator, location, language, copyright status, or any other terms) with documents, making the new enhanced documents searchable
• Tools for Web site management: Large Web sites can be managed dynamically according to content categories customized for the site managers
• Software that takes advantage of both RDF and OWL: Organizations can integrate enterprise applications, publishing and subscriptions using flexible models
• Cross-application data reuse: RDF and OWL formats are standard, not proprietary, allowing data reuse from diverse sources

Many specific examples of commercial applications and enterprise scale implementations of these technologies are detailed in both the testimonial page, and the RDF Implementations and OWL Implementations pages.

How the Semantic Web Pieces Fit Together -- XML, RDF and OWL

Much has been written about the Semantic Web, as if it is a replacement technology for the Web we know today. "In reality," countered Eric Miller, W3C Semantic Web Activity Lead, "it's more Web Evolution than Revolution. The Semantic Web is made through incremental changes, by bringing machine-readable descriptions to the data and documents already on the Web. XML, RDF and OWL enable the Web to be a global infrastructure for sharing both documents and data, which make searching and reusing information easier and more reliable as well."

W3C's Semantic Web Activity builds on work done in other W3C Activities, such as the XML Activity. Its focus is to develop standard technologies, on top of XML, that support the growth of the Semantic Web.

XML Provides Rules, Syntax for Structured Documents

At the foundation, XML provides a set of rules for creating vocabularies that can bring structure to both documents and data on the Web. XML gives clear rules for syntax; XML Schemas then serve as a method for composing XML vocabularies. XML is a powerful, flexible surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents.

RDF Delivers a Data Framework for the Web

RDF -- the Resource Description Framework -- is a standard a way for simple descriptions to be made. What XML is for syntax, RDF is for semantics: a clear set of rules for providing simple descriptive information. RDF Schema then provides a way for those descriptions to be combined into a single vocabulary. RDF is integrated into a variety of applications including:

• library catalogs
• world-wide directories
• syndication and aggregation of news, software, and content
• personal collections of music, photos, and events

In these cases, each uses XML as an interchange syntax. The RDF specifications provide a powerful framework for supporting the exchange of knowledge on the Web.

"RDF is part of the foundation of a major advance in the power of the Web. Ultimately, we will see users and applications combining information represented in RDF from multiple sources on the Web in ways that, until now, have been inconceivable," explains Brian McBride, Chair of the RDF Core Working Group, "The RDFCore Working Group has turned the RDF specifications into both a practical and mathematically precise foundation on which OWL and the rest of the Semantic Web can be built."

OWL Delivers Ontologies that Work on the Web

What's needed next is a way to develop subject -- or domain -- specific vocabularies. That is the role of an ontology. An ontology defines the terms used to describe and represent an area of knowledge. Ontologies are used by people, databases, and applications that need to share subject-specific (domain) information -- like medicine, tool manufacturing, real estate, automobile repair, financial management, etc. Ontologies include computer-usable definitions of basic concepts in the domain and the relationships among them. They encode knowledge in a domain and also knowledge that spans domains. In this way, they make that knowledge reusable.

OWL -- the Web Ontology Language -- provides a language for defining structured, Web-based ontologies which delivers richer integration and interoperability of data among descriptive communities. Where earlier languages have been used to develop tools and ontologies for specific user communities (particularly in the sciences and in company-specific e-commerce applications), they were not defined to be compatible with the architecture of the World Wide Web in general, and the Semantic Web in particular.

OWL uses both URIs for naming and the description framework for the Web provided by RDF to add the following capabilities to ontologies:

• Ability to be distributed across many systems
• Scalability to Web needs
• Compatibility with Web standards for accessibility and internationalization
• Openness and extensibility

OWL builds on RDF and RDF Schema and adds more vocabulary for describing properties and classes: among others, relations between classes (e.g., disjointness), cardinality (e.g., "exactly one"), equality, richer typing of properties, characteristics of properties (e.g., symmetry), and enumerated classes.

"OWL takes a major step forward in representing and organizing knowledge on the World Wide Web. It strikes a sound balance between the needs of industry participants for a language which addresses their current Web use cases, and the restrictions on developing an ontology language that meshed with established scientific principles and research experience," explained Jim Hendler and Guus Schreiber, co-chairs for the Web Ontology Working Group. "Over fifty Working Group members have successfully designed a language that addresses both sets of concerns and is endorsed by academics and practitioners alike."