Chapter 1 Computing with Services ServiceOriented Computing Semantics

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

Highlights of this Chapter n n n Chapter 1 Visions for the Web Open Environments Services Introduced The Evolving Web Standards Bodies Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 2

System Architectures: Centralized Terminal 3270 Terminal Mainframe Terminal Terminal Chapter 1 Terminal Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 3

System Architectures: Client-Server PC Client E-Mail Server Workstation Client Web Server PC Client Database Server Master-Slave Chapter 1 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 4

The Web As It Is Not easy to program n Designed for people to get information n Supports low-level interactions n n n Chapter 1 Focuses on visual display (as in HTML) Lacks support for meaning 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 5

System Architectures: Peer-to-Peer Application E-Mail System Chapter 1 Web System Database System Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 6

System Architectures: Cooperative Agent Application Agent E-Mail System (Mediators, Proxies, Aides, Wrappers) Chapter 1 Application Agent Web System Agent Database System Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 7

The Web As It Is Becoming n Enable interactions autonomous, heterogeneous parties (information providers and users) n n Chapter 1 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 8

Viewpoints on Services n Traditionally, a capability that is provided and exploited, often but not always remotely n n n Chapter 1 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 9

What is a (Web) Service? A piece of business logic accessible via the Internet using open standards (Microsoft) n Encapsulated, loosely coupled, contracted software functions, offered via standard protocols (Desti. Corp) n A set of interfaces providing a standard means of interoperating between different software applications, running on a variety of platforms and frameworks (W 3 C) Our working definition: A service is functionality that can be engaged n Chapter 1 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 10

Scope Includes wherever Internet and Web technologies are employed n Internet n Intranet: network restricted within an enterprise n Extranet: private network restricted to selected enterprises n Virtual Private Network (VPN): a way to realize an intranet or extranet over the Internet Chapter 1 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 11

Service Composition n Vision n n Obviously desirable and challenging But is this what we want? n n n Chapter 1 Specify and provide services independently, hiding implementations Use services in combination in novel ways Going beyond the idea of a passive object 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 12

Applications of Composable Services n n n Chapter 1 Portals Legacy system interoperation E-commerce Virtual enterprises Grid computing Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 13

Autonomy Independence of business partners (users and organizations) n Political reasons n n Ownership of resources Control, especially of access privileges Payments Technical reasons n Chapter 1 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 14

Heterogeneity Independence of component designers and system architects n Political reasons n n Ownership of resources Technical reasons n n n Chapter 1 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 15

Dynamism n n Independence of system administrators Needed because the parties change n n Architecture and implementation Behavior Interactions Make configurations dynamic to improve service quality and maintain flexibility Chapter 1 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 16

Locality: How to Handle the Above n n Reduce sharing of data and metadata to reduce inconsistencies and anomalies Reduce hard-coding, which reflects out-ofband agreements among programmers n n n Bind dynamically to components Use standardized formats to express data Express important knowledge as metadata Use standardized languages to express metadata Relax consistency constraints n n Chapter 1 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 17

Historical View of Services over the Web Generation Chapter 1 Scope Technology Example First All Second Programmatic Screen scraper Systematically generated HTML content Third Standardized Web services Formally described service Fourth Semantic Web services Semantically described service Fifth Collaborative Business protocols Service engagements Browser Any HTML page Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 18

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