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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.

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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. 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

  4. 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

  5. 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

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

  7. System Architectures: CooperativeAssume heterogeneity; agents handle interactions 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

  8. The Web As It Is Becoming • Enable interactions autonomous, heterogeneous parties (information providers and users) • Go beyond visual display to capture meaning  Semantically expressive 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

  9. 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

  10. 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

  11. 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

  12. Service Composition • Vision • Specify services independently of implementation • Compose (to reuse) services in novel ways • Go 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. Locality: Avoiding Remote Dependencies • 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 • Minimize need for remote knowledge • Correct rather than prevent violations of constraints: often feasible Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. Historical View of Services over the Web 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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