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Created: December 01, 2004.
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OWL Web Ontology Language for Services (OWL-S) Specification Submitted to W3C.

W3C has acknowledged receipt of a multi-part OWL-S Member Submission from France Telecom, Maryland Information and Network Dynamics Lab at the University of Maryland, National Institute of Standards and Technology (NIST), Network Inference, Nokia, SRI International, Stanford University, Toshiba Corporation, and University of Southampton.

The OWL Web Ontology Language for Services (OWL-S) specification represents "the first W3C member Submission in the area of Semantic Web Services, where Semantic Web technologies are applied to the challenges offered in the Web services arena." The submitters have requested that W3C consider OWL-S as input for work in a new Semantic Web Services working group at W3C.

The W3C OWL Web Ontology Language, approved as a W3C Recommendation in February 2004, 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."

An earlier version of the OWL-S specification was released for public review by members of the OWL Services Coalition in January 2004. Previous releases of this language were known as DAML-S, and were built upon DAML+OIL, the predecessor of OWL.

The OWL-S Member Submission proposes a framework based on the W3C OWL Web Ontology Language, designed "to help users and agents search, discover, invoke, compose and monitor Web services. It includes eight (8) ontologies written in OWL as an extensible core. In OWL-S, information used for Web service automation is exchanged in RDF — the same language the rest of the web is beginning to use for expressing data. Details of the OWL-S work have already been discussed extensively in the W3C Semantic Web Services Interest Group and the Semantic Web Services Initiative (SWSI)."

OWL-S, according to the Submission abstract, is "an OWL-based Web service ontology, which supplies a core set of markup language constructs for describing the properties and capabilities of Web services in unambiguous, computer-intepretable form. OWL-S markup of Web services will facilitate fuller automation of Web service tasks, such as Web service discovery, execution, composition and interoperation."

The OWL-S submission includes, in addition to the eight ontologies in .owl format, two expository documents. OWL-S: Semantic Markup for Web Services describes "the overall structure of the ontology and its three main parts: the service profile for advertising and discovering services; the process model, which gives a detailed description of a service's operation; and the grounding, which provides details on how to interoperate with a service, via messages." The second document, OWL-S' Relationship to Selected Other Technologies, characterizes the relationship of OWL-S to selected Web service and Semantic Web technologies, commenting briefly so as "to clarify the possible uses of OWL-S, and perhaps give some guidance as to its potential place in the realm of activities at W3C." Technologies discussed include WSDL, SOAP, UDDI, BPEL4WS, CDL, ebXML, Grid services, OWL and SWRL, and Web Services Modeling Ontology (WSMO).

OWL-S provides a framework of ontologies written in OWL (not a new ontology language, nor a version of OWL), comprised of three main OWL ontologies (Profile, Process, Grounding), a Service Ontology, and four additional ontologies serving supplementary roles (Logical Expression Constructs, List Constructs, Profile Additional Parameters, Actor Ontology).

The Service Ontology helps organize the three main OWL-S ontologies. The Profile ontology "is meant to be used by publishing and discovery applications, providing search and matchmaking. It includes expression of limitations, requirements, and quality of service." The Process ontology "describes the use of the service, detailing the semantic content of messages. This semantic description aims at helping composition, coordination, and execution monitoring of Web services." The Grounding ontology "is the link to the service's concrete realization. It defines a mapping of 'atomic processes' in OWL-S to WSDL input and output messages. This binding from the abstract, semantically-described processes to concrete exchanges specification is essential to begin integration with the existing Web services architecture."

The W3C Team Comment on the OWL-S submission says the Team "looks forward to new functionality and user benefits deriving from this emerging interoperability of data... We look forward to the Web services community providing feedback on the utility of the architecture and overall functionality offered by OWL-S. We also look forward to a discussion of the degree of interest that exists in integrating the OWL-S approach into the mainstream of Web services technologies, as well as the strategy and sequencing that could be put in place to accomplish this goal."

W3C plans to host a Semantic Web Services workshop in the first half of 2005, and "one possible outcome would be a Recommendation track on a Semantic Web Services framework."

From OWL-S: Semantic Markup for Web Services

The Semantic Web should enable greater access not only to content but also to services on the Web. Users and software agents should be able to discover, invoke, compose, and monitor Web resources offering particular services and having particular properties, and should be able to do so with a high degree of automation if desired. Powerful tools should be enabled by service descriptions, across the Web service lifecycle. OWL-S (formerly DAML-S) is an ontology of services that makes these functionalities possible.

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... 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..." [from the Introduction]

From the W3C Team Comment on the OWL-S Submission

The OWL-S Submission has a strong dependency on the Web Services Description Language (WSDL) 1.1 Submission. Several parts of this framework rely on mappings to WSDL: an "atomic process" in OWL-S corresponds to a WSDL 1.1 operation, sets of inputs/outputs used in such an atomic process map to WSDL messages, and types map to WSDL abstract types. The Grounding ontology achieves the link to WSDL. Additional coordinated work would be needed to transition OWL-S to use WSDL 2.0, which is currently under development.

The Profile ontology overlaps the area of constraints and capabilities, as discussed at the recent W3C workshop. Expressing conditions of use and applicability, as well as quality of service, represent a significant part of this issue.

The design of OWL-S also brings to Web services choreography and orchestration an approach to automated service composition, coordination, and cooperation based on description logic (OWL-DL). This work is related to the Web Services Choreography Description Language (WS-CDL).

The design of OWL-S poses some opportunities and challenges as a major early user of OWL and a potential user of a rule language. OWL-S currently uses Semantic Web Rule Language (SWRL) 0.6 in an experimental capacity. The Web services user base and use cases may help focus rule language activities within the W3C, which has staff involved in related research (cwm, metalog), supports mailing lists (www-rdf-rules, www-rdf-logic), and is in the early stages of planning a Semantic Web rule language workshop to be held in the first half of 2005..." [see the complete text]

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