SEMANTICS WEB SERVICES

The inventor of the World Wide Web, Tim Berners-Lee, is also the originator of the next generation of Web architecture, the Semantic Web. Currently, his World Wide Web consortium (W3C) team works to develop, extend, and standardize the Web's markup languages and tools.

The objective of the Semantic Web Architecture is to provide a knowledge representation of linked data in order to allow machine processing on a global scale. The W3C has developed a new generation of open standard markup languages that are now poised to unleash the power, flexibility and, above all, logic of the next generation of the Web, and open the door to the next generation of Web Services.

Currently, Web Services that use the .NET and J2EE frameworks are struggling to expand against the limitations of existing Web architecture and conflicting proprietary standards. With software vendors battling for any advantage, Semantic Web Services offer a giant leap forward; the first-time developer can successfully exploit its latent potential to deliver such applications as semantic search, collective email and collaborative Web word processing.

For Semantic Web services to become a reality, a markup language must be descriptive enough that a computer can automatically determine its meaning. The following is a list of tasks such a language would be required to perform:

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• Discovery: A program must first be able to automatically find, or discover, an appropriate Web service. Neither the Web Service Description Language (WSDL) nor the Universal Discovery and Description language (UDDI) allows for software to determine what a Web service offers to the client. A Semantic Web service describes its properties and capabilities so that software can automatically determine its purpose.
• Invocation: Software must be able automatically to determine how to invoke or execute the service. For example, if executing the service is a multi-step procedure, the software needs to know how to interact with the service to complete the necessary sequence. A Semantic Web service provides a descriptive list of what an agent needs to do to be able to execute and fulfill the service. This includes defining the inputs and outputs of the service.
• Composition: Software must be able to select and combine a number of Web services to complete a certain objective. The services have to interoperate with each other seamlessly so that the combined results are a valid solution.
• Monitoring: Agent software needs to be able to verify and monitor the service properties while in operation.

When Web markup languages evolve to the point that they can perform the above tasks, Semantic Web service can begin to prosper. You may be surprised to learn just how near the W3C is to meeting these conditions.

Advanced Markup Languages

There are many ways in which the two areas of Web Services and the Semantic Web could interact to lead to the further development of Semantic Web Services. Berners-Lee has suggested that both of these technologies would benefit from integration that would combine the Semantic Web's meaningful content with Web Services' business logic.

Areas such as UDDI and WSDL are ideally suited to be implemented using Semantic Web technology. In addition, SOAP could use Resource Description Framework (RDF) payloads, remote RDF queries and updates, and interact with Semantic Web business rules engines, thereby laying the foundation for Semantic Web Services.

The W3C is engaged in building the Pyramid of Web Markup Languages, which starts with HTML and XML and continues upward to include RDF and the most recent Web Ontology Language (OWL). The off-spring of OWL is OWL for Services (OWL-S).

However, the technology issues of the Next Generation Web create many problematic questions that must be solved before the full power and capability of the Semantic Web Services are available.

Semantic Web Services

Semantic Web Technology

• allow machine supported data interpretation
• ontologies as data model

Web Service Technology

• automated discovery, selection, composition,
• and web-based execution of services.

=> Semantic Web Services as integrated solution for realizing the vision of the next generation of the Web

• define exhaustive description frameworks for describing Web Services and related aspects (Web Service Description Ontologies)
• support ontologies as underlying data model to allow machine supported data interpretation (Semantic Web aspect)
• define semantically driven technologies for automation of the Web Service usage process (Web Service aspect) .

Usage Process:

• Publication: Make available the description of the capability of a service
• Discovery: Locate different services suitable for a given task
• Selection: Choose the most appropriate services among the available ones
• Composition: Combine services to achieve a goal
• Mediation: Solve mismatches (data, protocol, process) among the combined
• Execution: Invoke services following programmatic conventions

Execution support:

• Monitoring: Control the execution process
• Compensation: Provide transactional support and undo or mitigate unwanted effects
• Replacement: Facilitate the substitution of services by equivalent ones
• Auditing: Verify that service execution occurred in the expected way

The Web Service Modeling Ontology WSMO

• Aims & Working Groups
• Design Principles
• • Top Level Notions
  • – Ontologies
  • – Web Services
  • – Goals
  • – Mediators
• • Comparison to OWL-S

WSMO is ..

• a conceptual model for Semantic Web Services:
• • – ontology of core elements for Semantic Web Services
  • – a formal description language (WSML)
  • .– execution environment (WSMX)
  • – derived from and based on the Web Service Modeling Framework WSMF
• • a SDK-Cluster Working Group

(joint European research and development initiative)

WSMO Working Groups

WSMO Design Principles

• Web Compliance
• Ontology-Based
• Goal-driven
• Strict Decoupling
• Centrality of Mediation
• Description versus Implementation
• Execution Semantics

Semantic Web Service:

Semantic Web services (SWS) has been a vigorous technology research area for about six years. A great deal of innovative work has been done, and a great deal remains. Several large research initiatives have been producing substantial bodies of technology, which are gradually maturing. SOA vendors are looking seriously at semantic technologies and have made initial commitments to supporting selected approaches.

In the world of standards, numerous activities have reflected the strong interest in this work. Perhaps the most visible of these is SAWSDL.1 SAWSDL recently achieved Recommendation status at the World Wide Web Consortium.

SAWSDL’s completion provides a fitting opportunity to reflect on the state of the art and practice in SWS—past, present, and future. This two-part installment of Trends & Controversies discusses what has been accomplished in SWS, what value SWS can ultimately provide, and where we can go from here to reap these technologies’ benefits.

SWS overview

As its name indicates, SWS lies at the intersection of two important trends in the World Wide Web’s evolution. The first is the rapid development of Web service technologies, whose long-term promise is to make the Web support shared activities (such as transactions, processes, and the formation of virtual organizations) as well as it supports shared information. In the shorter term, the driving objective behind Web services has been reliable, vendor-neutral software interoperability across platforms, networks, and organizations. A related objective has been the ability to coordinate business processes involving heterogeneous components (deployed as services) across ownership boundaries. These objectives, in turn, have led to the development of widely recognized Web service standards such as WSDL, UDDI, and BPEL.

The second trend—the Semantic Web—focuses on the publication of more expressive metadata in a shared knowledge framework, enabling the deployment of software agents that can intelligently use Web resources.2 Essentially, the Semantic Web brings knowledge-representation languages and ontologies into the fabric of the Internet, providing a foundation for powerful new approaches to organizing, describing, searching for, and reasoning about information and activities on the Web (or other networked environments).

The central theme of SWS, then, is the use of richer, more declarative descriptions of the elements of dynamic distributed computation—services, processes, message-based conversations, transactions, and so on. These descriptions, in turn, enable fuller, more flexible automation of service provision and use and the construction of more powerful tools and methodologies for working with services.

Because a rich representation framework permits a more comprehensive specification of many aspects of services, SWS can provide a solid foundation for a broad range of activities throughout the Web service life cycle. For example, richer service descriptions can support

• * greater automation of service selection and invocation,
• * automated translation of message content between heterogeneous interoperating services,
• * automated or semiautomated approaches to service composition, and
• * more comprehensive approaches to service monitoring and recovery from failure.

Farther down the road, richer semantics can help automate such activities as verification, simulation, configuration, supply chain management, contracting, and service negotiation. This applies not only to the Internet at large but also within organizations and virtual organizations.

SWS research, as a distinct field, began in earnest in 2001. A 2001 article in this magazine by Sheila A. McIlraith, Tran Cao Son, and Honglei Zeng was perhaps the first to point out the potential and importance of bringing Semantic Web techniques to services.3 Earlier work, however, had considered the construction of knowledge-intensive applications on the fly from online problem-solving methods.4 Also in 2001, the initial release of OWL-S (originally DAML-S) became available.5 Other major initiatives began not long thereafter, including WSMO,6 SWSF,7 WSDL-S,8 and the Internet Reasoning Service.9 But it would be a mistake to consider only these larger, coordinated research efforts. Individual researchers and small teams have also done much valuable work, sometimes drawing on one of these larger efforts, sometimes not.

SWS aim to bring Semantic Web technology—for representing, sharing, and reasoning about knowledge—to bear in Web service contexts. The objective is to enable a fuller, more flexible automation of service provision and use and the construction of more powerful tools and methodologies for working with services.