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

Chapter 1 2Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

Highlights of this Chapter

Visions for the Web Open Environments Services Introduced The Evolving Web Standards Bodies

Chapter 1 3Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 4Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 5Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

Historical View of Services over the Web

Generation

Scope Technology

Example

First All Browser Any HTML page

Second Programmatic

Screen scraper

Systematicallygenerated HTMLcontent

Third Standardized

Web services

Formally described service

Fourth Semantic Semantic Web services

Semantically described service

Chapter 1 6Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 7Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 8Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 9Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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?

Chapter 1 10Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

Applications of Composable Services

Portals Legacy system interoperation E-commerce Virtual enterprises Grid computing

Chapter 1 11Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 12Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 13Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 14Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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

Chapter 1 15Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

System Architectures: Centralized

Mainframe

Terminal3270

Terminal

Terminal

Terminal

Terminal

TerminalTerminal

Terminal

Terminal

Terminal

Terminal

Chapter 1 16Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

System Architectures: Client-Server

E-MailServer

WebServer

DatabaseServer

PCClient

PCClient PC

Client

WorkstationClient

Master-Slave

Chapter 1 17Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

System Architectures: Peer-to-Peer

E-MailSystem

WebSystem

DatabaseSystem

Application

ApplicationApplication

Application

Chapter 1 18Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

System Architectures: Cooperative

E-MailSystem

WebSystem

DatabaseSystem

Application

ApplicationApplication

Application

(Mediators, Proxies, Aides, Wrappers)

Agent

Agent

Agent

Agent

Agent

Agent

Agent

Agent

Chapter 1 19Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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