Transcript Chapter 1: Computing with Services Service-Oriented Computing: Semantics, Processes, Agents

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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Visions for the Web
Open Environments
Services Introduced
The Evolving Web
Standards Bodies
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The Web As Is
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Designed for people to get information
Sources are independent and
heterogeneous
Limitations
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HTML describes how things appear
HTTP is stateless
Processing is asynchronous client-server
No support for integrating information
No support for meaning and understanding
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Web Semantics
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“The Semantic Web” is Tim Berners-Lee’s vision
Human  Machine  Agents
Client-Server  P2P  Cooperative
Syntax  Semantics  Mutual Understanding  Pragmatics
and Cognition
Future Web Services:
focus on organization and society
Data  Services  Processes
Pragmatics (getting work done) Distributed Cognition
- Workflows, BPEL4WS
- Decisions and Plans
Semantics and Understanding
- Ontologies, OWL
Syntax, Language, and Vocabulary
- FIPA ACL
Current Web Services:
focus on individual and small group
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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 over the web (DestiCorp)
 A set of interfaces, which provide a standard
means of interoperating between different
software applications, running on a variety of
platforms and/or frameworks (W3C)
Our working definition: A WS is functionality
that can be engaged over the Web
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Viewpoints on Services
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Networking: a service is characterized by bandwidth and
suchlike properties.
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Telecommunications: Narrow telephony features such as caller
ID and call forwarding, and basic connection services like
narrowband versus broadband (itself of a few varieties).
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Systems: Services are for billing and storage and other key
operational functions. These functions are often parceled up in
the so-called operation-support systems.
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Web applications: Services correspond to Web pages, especially
those with forms or a programmatic interface thereto.
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Wireless: Wireless versions of the Web, but also things like
messaging, as in the popular short message service (SMS).
If there is agreement here, it is that a service is a capability that is
provided and exploited, often but not always remotely.
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Brief History of Information
Technology
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System Architectures: Centralized
Terminal
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Terminal
Terminal
Terminal
Terminal
Mainframe
Terminal
Terminal
Terminal
Terminal
Terminal
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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
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System Architectures: Peer-to-Peer
Application
Application
Application
Application
E-Mail
System
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Web
System
Database
System
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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)
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Kinds of Networks
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
When we talk about Internet computing or Web
services, we consider all of the above as possible
environments
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Open Environments: Characteristics
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Cross enterprise boundaries or
administrative domains
Comprise autonomous resources that
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Involve loosely structured addition and removal
Range from weak to subtle consistency
requirements
Involve updates only under local control
Frequently involve nonstandard data
Have intricate interdependencies
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Autonomy (Usage)
Independence of business partners
(users)
 Political reasons
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Ownership of resources
Control, especially of access privileges
Payments
Technical reasons
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Opacity of systems with respect to key
features, e.g., precommit
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Heterogeneity (Construction)
Independence of component designers and
system architects
 Political reasons
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Ownership of resources
Technical reasons
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Conceptual problems in integration
Fragility of integration
Difficult to guarantee behavior of integrated
systems
Best not to assume homogeneity
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Dynamism (Configuration)
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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
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Locality
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Global information (data, schemas, constraints)
causes
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Global information is essential for coherence
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Inconsistencies
Anomalies
Difficulties in maintenance
Locations of services or agents
Applicable business rules
Relaxation of constraints works often
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Obtain other global knowledge only when needed
Correct rather than prevent violations of constraints: often
feasible
When, where, and how of corrections must be specified, but
it is easier to make it local
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Historical View of Services over the Web
Generation
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Scope
Technology
Example
First
All
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Programmatic Screen
scraper
Systematically
generated HTML
content
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Standardized
Web services
Formally
described service
Fourth
Semantic
Semantic
Web services
Semantically
described service
Browser
Any HTML page
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The Evolving Web
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Near Web: conventional mouse-keyboard-monitor
interaction with a personal computer, typically for
purposes such as surfing the Web
Far Web: interaction with a computer from across a
room as with a TV remote control, typically for
entertainment, such as listening to music or viewing
a movie
Here Web: interaction with a mobile device, with
narrow bandwidths for input and output
Weird Web: interaction through emerging interface
technologies, such as voice and wearable computing
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Applications of Services
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Services should be composable
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Portals
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Provided independently
Used in novel, unanticipated ways
Organized by topic or affinity
Best when personalized
E-commerce
Legacy system integration
Virtual enterprises
Grid computing
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Chapter 1 Summary
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Evolving perspectives on the Web
Evolutions in IT architectures
Key aspects of open environments
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Autonomy
Heterogeneity
Dynamism
Services, if understood correctly, can
support IT in open environments
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