chapter 1: computing with services service-oriented computing: semantics, processes, agents –...
TRANSCRIPT
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 Is
Designed for people to get information
Sources are independent and heterogeneous
Limitations HTML describes how things appear HTTP is stateless Processing is asynchronous client-server No support for integrating information No support for meaning and
understanding
Chapter 1 4Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Web Semantics “The Semantic Web” is Tim Berners-Lee’s vision Human Machine Agents Client-Server P2P Cooperative Syntax Semantics Mutual Understanding
Pragmatics and Cognition Data Services Processes
Syntax, Language, and Vocabulary- FIPA ACL
Semantics and Understanding- Ontologies, OWL
Pragmatics (getting work done)- Workflows, BPEL4WS
Distributed Cognition- Decisions and Plans
Current Web Services:focus on individual and small group
Future Web Services:focus on organization and society
Chapter 1 5Service-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 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
Chapter 1 6Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Viewpoints on Services Networking: a service is characterized by bandwidth and
suchlike properties. Telecommunications: Narrow telephony features such as
caller ID and call forwarding, and basic connection services like narrowband versus broadband (itself of a few varieties).
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.
Web applications: Services correspond to Web pages, especially those with forms or a programmatic interface thereto.
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.
Chapter 1 7Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Brief History of Information Technology
Chapter 1 8Service-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 9Service-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 10Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
System Architectures: Peer-to-Peer
E-MailSystem
WebSystem
DatabaseSystem
Application
ApplicationApplication
Application
Chapter 1 11Service-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 12Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
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 InternetWhen we talk about Internet computing or Web
services, we consider all of the above as possible environments
Chapter 1 13Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Open Environments: Characteristics
Cross enterprise boundaries or administrative domains
Comprise autonomous resources that 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
Chapter 1 14Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Autonomy (Usage)
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
Chapter 1 15Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Heterogeneity (Construction)
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
systemsBest not to assume homogeneity
Chapter 1 16Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Dynamism (Configuration)
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 17Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Locality
Global information (data, schemas, constraints) causes
Inconsistencies Anomalies Difficulties in maintenance
Global information is essential for coherence Locations of services or agents Applicable business rules
Relaxation of constraints works often 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
Chapter 1 18Service-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 19Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
The Evolving Web 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
Chapter 1 20Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Applications of Services
Services should be composable Provided independently Used in novel, unanticipated ways
Portals Organized by topic or affinity Best when personalized
E-commerce Legacy system integration Virtual enterprises Grid computing
Chapter 1 21Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and
Michael Huhns
Chapter 1 Summary
Evolving perspectives on the Web Evolutions in IT architectures Key aspects of open environments
Autonomy Heterogeneity Dynamism
Services, if understood correctly, can support IT in open environments