The Semantic Web is a “web of data” that enables machines to understand the semantics, or meaning, of information on the World Wide Web.It extends the network of hyperlinked human-readable web pages by inserting machine-readable metadata about pages and how they are related to each other, enabling automated agents to access the Web more intelligently and perform tasks on behalf of users. The term was coined by Tim Berners-Lee, the inventor of the World Wide Web and director of the World Wide Web Consortium, which oversees the development of proposed Semantic Web standards. He defines the Semantic Web as “a web of data that can be processed directly and indirectly by machines.”
The term “Semantic Web” is often used more specifically to refer to the formats and technologies that enable it. These technologies include the Resource Description Framework (RDF), a variety of data interchange formats (e.g. RDF/XML, N3, Turtle, N-Triples), and notations such as RDF Schema (RDFS) and the Web Ontology Language (OWL), all of which are intended to provide a formal description of concepts, terms, and relationships within a given knowledge domain.
Many of the technologies proposed by the W3C already exist and are used in various contexts, particularly those dealing with information that encompasses a limited and defined domain, and where sharing data is a common necessity, such as scientific research or data exchange among businesses. In addition, other technologies with similar goals have emerged, such as microformats. However, the Semantic Web as originally envisioned, a system that enables machines to understand and respond to complex human requests based on their meaning, has remained largely unrealized and its critics have questioned its feasibility.
Efforts toward the creation of the Semantic Web are gaining momentum. Soon it will be possible to access Web resources by content rather than just by keywords. A significant force in this movement is the development of a new generation of Web markup languages such as OWL and its predecessor DAML+OIL. These languages enable the creation of ontologies for any domain and the instantiation of these ontologies in the description of specific Web sites. These languages are also amenable to efficient reasoning procedures and thus reasoning applications can be built to automatically determine the logical consequences of the ontological statements.
Among the most important Web resources are those that provide services. By “service” we mean Web sites that do not merely provide static information but allow one to effect some action or change in the world, such as the sale of a product or the control of a physical device. The Semantic Web should enable users to locate, select, employ, compose, and monitor Web-based services automatically.
To make use of a Web service, a software agent needs a computer-interpretable description of the service, and the means by which it is accessed. An important goal for Semantic Web markup languages, then, is to establish a framework within which these descriptions are made and shared. Web sites should be able to employ a standard ontology, consisting of a set of basic classes and properties, for declaring and describing services, and the ontology structuring mechanisms of OWL provide an appropriate, Web-compatible representation language framework within which to do this.
This paper describes a collaborative effort by researchers at several organizations to define just such an ontology. We call this ontology OWL-S. In what follows, we will first motivate OWL-S in terms of some sample tasks that it is designed to support. In the central part of the paper we describe the upper ontology for services that we have developed, including its subontologies for profiles, processes, and groundings. The ontology is still evolving, and making connections to other development efforts, such as those building ontologies of time and resources. We will sometimes refer to the OWL-S ontology as a language for describing services, reflecting the fact that it provides a standard vocabulary that can be used together with the other aspects of the OWL description language to create service descriptions.
This paper reflects the authors’ design consensus as of OWL-S version 1.1. Please note that, in addition to the OWL ontology files, the release site includes examples and additional forms of documentation, including, in particular, a code walk-through illustrative of many points in this document, additional explanatory material (in HTML) regarding the grounding and the use of profile-based class hierarchies, and information about the status of this work, including unresolved issues and future directions.
For more information about Semantic Markup and its role in determining the future of web design, visit w3c.org.
