Download Chapter 1: Computing with Services

Computing with Services
CS 696 – Services Computing
Fall 2008
Chapter 1, Service-Oriented Computing:
Semantics,
Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005
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Highlights of this Chapter
(1)
(2)
(3)
(4)
(5)
Visions for the Web
Open Environments
Services Introduced
The Evolving Web
Standards Bodies
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(1) Visions for the Web
- 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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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
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
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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(2) 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)
The Components in an environment function
solely under their own control.
Independence of business partners (users)
 Political reasons
 Ownership of resources
 Control, especially of access privileges
 Payments
 Technical reasons
 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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(3) Services Introduced
Historical View of Services over the Web
Generation
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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(4) 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
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The Evolving Web (conti)
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Weird Web: interaction through
emerging interface technologies, such
as voice and wearable computing
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B2B Web: dealing with the supply
networks of business-to-business
electronic commerce
Pervasive Web: dealing with deviceto-device interactions
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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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(5) Standards Bodies
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The following are the most important stanards bodies
and initiatives for services.
IETF – The Internet Engineering Task Force
TCP/IP Suite and URIs, HTTP, SIP, SMTP
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OMG – The Object Management Group
UML, CORBA, MDA
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W3C – The World Wide Web Consortium
XML, XML Schema, WSDL, SOAP, and WSCI
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OASIS – The Organization for the Advancement of
Structured Information Standards
Universal Business Language (UBL), UDDI, and the Business
Process Execution Language for Web Services (BPEL4WS)
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Standards Bodies (Conti)
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UN/CEFACT – The United Nations Center for Trade
Facilitation and Electronic Business - ebXML
WS-L – The Web Services Interoperability
Organization - BP 1.0
BPMLorg - The Business Process Management
Initiative - Business Process Modeling Language (BPML)
WfMC - The Workflow Management Coalition
FIPA – The Foundation for Intelligent Physical
Agents promotes technologies and specifications
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Standards for Web Services
ebXML
Registries Discovery
UDDI
ebXML
CPA
OWL-S Service
Model
OWL-S
Service
WSCL
Profile
OWL-S Service
Grounding
OWL
RDF
PSL
BPEL4WS
BPML
WS-AtomicTransaction and WSXLANG
BusinessActivity
WS-Reliable
WS-Coordination
Messaging
WS-Security
WSCL
WS-Policy
WSDL
SOAP
BTP
WSCI
ebXML
BPSS
Contracts and
agreements
Process and workflow
orchestrations
QoS: Transactions
QoS: Choreography
QoS: Conversations
ebXML QoS: Service
CPP
descriptions and bindings
ebXML
messaging Messaging
XML, DTD, and XML Schema
Encoding
HTTP, FTP, SMTP, SIP, etc.
Transport
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XML Web Service Foundation
Open and with broad industry support
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Publish, Find, Use Services
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Service Interactions
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WSDL
Ubiquitous Communications
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XML
Description Language
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SOAP
Universal Data Format
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UDDI
TCP/IP, HTTP, SMTP, SIP, Reliable messaging
Security (authentication and authorization)
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WS-Security, SAML
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eXtensible Markup Language (XML)
Simple Object Access Protocol (SOAP)
Web Services Description Language
(WSDL)
Directory Services
Universal Description, Discovery, and
Integration (UDDI)
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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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