Chapter 1:
Computing with Services
Service-Oriented Computing: Semantics, Processes, Agents
– Munindar P. Singh and Michael N. Huhns, Wiley, 2005
Highlights of this Chapter
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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
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The Web As It Is
Not easy to program
 Designed for people to get information
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Supports low-level interactions
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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
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The Web As It Is Becoming
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Enable interactions autonomous,
heterogeneous parties (information
providers and users)
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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
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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
Semantic
Web services
Semantically
described service
Browser
Any HTML page
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Viewpoints on Services
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Traditionally, a capability that is provided and
exploited, often but not always remotely
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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
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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
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Chapter 1
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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
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Service Composition
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Vision
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Obviously desirable and challenging
But is this what we want?
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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?
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Applications of Composable Services
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Chapter 1
Portals
Legacy system interoperation
E-commerce
Virtual enterprises
Grid computing
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Autonomy
Independence of business partners (users
and organizations)
 Political reasons
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Ownership of resources
Control, especially of access privileges
Payments
Technical reasons
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Chapter 1
Opacity of systems with respect to key
features, e.g., precommit in distributed
databases
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Heterogeneity
Independence of component designers
and system architects
 Political reasons
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Ownership of resources
Technical reasons
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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
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Dynamism
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Independence of system administrators
Needed because the parties change
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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
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Locality: How to Handle the Above
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Reduce sharing of data and metadata to
reduce inconsistencies and anomalies
Reduce hard-coding, which reflects out-ofband agreements among programmers
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Bind dynamically to components
Use standardized formats to express data
Express important knowledge as metadata
Use standardized languages to express metadata
Relax consistency constraints
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Chapter 1
Obtain remote knowledge only when needed
Correct rather than prevent violations of
constraints: often feasible
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System Architectures: Centralized
Terminal
3270
Terminal
Terminal
Terminal
Terminal
Mainframe
Terminal
Terminal
Terminal
Terminal
Terminal
Chapter 1
Terminal
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System Architectures: Client-Server
PC
Client
E-Mail
Server
Workstation
Client
Web
Server
PC
Client
PC
Client
Database
Server
Master-Slave
Chapter 1
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System Architectures: Peer-to-Peer
Application
Application
Application
Application
E-Mail
System
Chapter 1
Web
System
Database
System
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
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System Architectures: Cooperative
Agent
Application
Application
Application
Agent
Agent
Agent
Application
Agent
E-Mail
System
Agent
Agent
Web
System
Agent
Database
System
(Mediators, Proxies, Aides, Wrappers)
Chapter 1
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Chapter 1 Summary
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Evolving perspectives on the Web
Evolutions in IT architectures
Open environments challenge some
fundamental assumptions of computer
science
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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
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Chapter 1: Computing with Services