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Chapter 1: Computing with Services

Chapter 1: Computing with Services. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. Visions for the Web Open Environments Services Introduced The Evolving Web Standards Bodies. The Web As It Is.

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Chapter 1: Computing with Services

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  1. Chapter 1:Computing with Services Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

  2. Highlights of this Chapter • Visions for the Web • Open Environments • Services Introduced • The Evolving Web • Standards Bodies Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  3. The Web As It Is Not easy to program • Designed for people to get information • Focuses on visual display (as in HTML) • Lacks support for meaning • Supports low-level interactions • HTTP is stateless • Processing is client-server • Creates avoidable dependencies among what should be independent components Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  4. The Web As It Is Becoming • Enable interactions autonomous, heterogeneous parties (information providers and users) • Go beyond visual display to capture meaning  Semantic Web • Support standardized interfaces  Web services • Support complex activities  processes • Support rich interactions among autonomous parties  agents Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  5. Historical View of Services over the Web Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  6. Viewpoints on Services • Traditionally, a capability that is provided and exploited, often but not always remotely • Networking: bundle of bandwidth-type properties • Telecom: features (caller ID, forwarding) • Systems: operational functions (billing, storage); parceled up into operation-support systems • Web or Grid: Web pages or Grid resources • Wireless: Wireless access; messaging • By contrast, we treat services as resembling real-life services or business partners Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  7. What is a Web Service? • A piece of business logic accessible via the Internet using open standards (Microsoft) • Encapsulated, loosely coupled, contracted software functions, offered via standard protocols (DestiCorp) • A set of interfaces providing a standard means of interoperating between different software applications, running on a variety of platforms and frameworks (W3C) Our working definition: A service is functionality that can be engaged Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  8. Scope Includes wherever Internet and Web technologies are employed • Internet • Intranet: network restricted within an enterprise • Extranet: private network restricted to selected enterprises • Virtual Private Network (VPN): a way to realize an intranet or extranet over the Internet Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  9. Service Composition • Vision • Specify and provide services independently, hiding implementations • Use services in combination in novel ways • Going beyond the idea of a passive object • Obviously desirable and challenging • But is this what we want? • Can or should implementations be hidden? • What about organizational visibility? • How to assess risk? How to handle exceptions? Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  10. Applications of Composable Services • Portals • Legacy system interoperation • E-commerce • Virtual enterprises • Grid computing Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  11. Autonomy Independence of business partners (users and organizations) • Political reasons • Ownership of resources • Control, especially of access privileges • Payments • Technical reasons • Opacity of systems with respect to key features, e.g., precommit in distributed databases Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  12. Heterogeneity Independence of component designers and system architects • Political reasons • Ownership of resources • Technical reasons • Conceptual problems in integration • Fragility of integration • Difficult to guarantee behavior of integrated systems Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  13. Dynamism • Independence of system administrators • Needed because the parties change • Architecture and implementation • Behavior • Interactions • Make configurations dynamic to improve service quality and maintain flexibility Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  14. Locality: How to Handle the Above • Reduce sharing of data and metadata to reduce inconsistencies and anomalies • Reduce hard-coding, which reflects out-of-band agreements among programmers • Bind dynamically to components • Use standardized formats to express data • Express important knowledge as metadata • Use standardized languages to express metadata • Relax consistency constraints • Obtain remote knowledge only when needed • Correct rather than prevent violations of constraints: often feasible Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  15. System Architectures: Centralized Terminal 3270 Terminal Terminal Terminal Terminal Mainframe Terminal Terminal Terminal Terminal Terminal Terminal Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  16. System Architectures: Client-Server Workstation Client PC Client PC Client PC Client E-Mail Server Web Server Database Server Master-Slave Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  17. System Architectures: Peer-to-Peer Application Application Application Application E-Mail System Web System Database System Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. System Architectures: Cooperative Agent Application Application Application Agent Agent Agent Application Agent Agent E-Mail System Agent Agent Database System Web System (Mediators, Proxies, Aides, Wrappers) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  19. Chapter 1 Summary • Evolving perspectives on the Web • Evolutions in IT architectures • Open environments challenge some fundamental assumptions of computer science • Autonomy • Heterogeneity • Dynamism • Services, if understood correctly, can support IT in open environments Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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