Transcript Introduction to Web Services

Introduction
CSIE, Da-Yeh University
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History of Software Development
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Traditional Programming Paradigm
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Structured Programming (1970’s)
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Behind schedule, costly, and unreliable.
Systematical analysis of the problems.
Does not mirror the real world entities.
Object Oriented Programming (1980’s – 1990’s)
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Object technique is a packaging scheme to create
software units.
Use classes to represent the real world entities.
Web service take advantages of the OO technology.
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Component-based Development
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A component is a piece of software that satisfies
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It must be deployable on its own
It must publish and adhere to a programming interface.
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Component-based Development
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The limitation of using components
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It takes a lot more effort to develop components that is
reusable.
It is difficult to find the right components.
It is hard to coordinate the releases of new components.
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Client Server Design
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Internet Design
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Application Server Architecture
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Distributed Computing
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The computing tasks are distributed over networks.
Components extended at different computers must be
able to communicate with each other.
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Interface and response
Security
Client
Proxy
Client
Proxy
Infrastructure
Application
internet
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Distributed Computing
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Different technology
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Object Management Group (OMG) – Common Object
Request Broker Architecture (CORBA)
Microsoft – Distributive Component Object Model
(DCOM)
IBM – Distributive System Object Model (DSOM)
Sun Micro – Remote Method Invocation (RMI)
Components from different technology communicate
with each other through a bridge.
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COM/CORBA bridge
Poor interoperability
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Distributed Computing Infrastructure
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Microsoft’s DCOM
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Shipped with versions of Windows NT beginning with
version 4.0 and including Windows 2000.
Provide both local and remote COM capabilities. It is
now an inherent part of Win32-based platforms.
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N-tier Web-based Application
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The client-tier uses browsers as the user interface.
The middle-tier provides all the business logic and
processes.
The information-tier is the information tier.
Client-tier
Middle-tier
data
Information-tier
data
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Alternative to Web Service
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Screen Scraping: retrieving data from other HTML
documents.
What are the disadvantages of using screen scraping?
Middle Tier
Application
Database
Web page
HTML
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Web Service Technology
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Address the issue of poor interoperability.
Use open standard.
Easy to debug.
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Web services use text-based protocols.
Use XML as the standard for exchanging information.
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Definition of Web Service
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Web services are software programs that use XML to
exchange information with other software via internet
protocol.
Characteristics of web service
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Web services are programmable.
Web services are based on XML.
Web services are self-describing (WSDL).
Web services are discoverable (UDDI).
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Web Service Architecture Protocols
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The core principles drive the design and
implementation of WS architecture protocols
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Message orientation
Protocol composability
Autonomous services
Managed transparency
Protocol-based integration
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Benefits over Distributed Computing
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Companies can expose and access web services using
technology already in place.
Web service is more interoperable.
Nearly all major software vendors have agreed to use
the same core standards.
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Challenge of the Web Service
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SOAP, WSDL, UDDI are still in draft.
Royalty fees may required for some standards.
Lack of standard security procedure.
Defining and guaranteeing QoS.
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Slow response time
Infrequent update
Inability to handle large number of requests
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Web Service Architecture
UDDI
Registry
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WSDL
Document
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1
4
client
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Query Registry to locate service
Refer to WSDL documents
Access WSDL documents
Provide data to interact with web
service
 Send SOAP message request
 Send SOAP message response
Web
Service
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Web Service Terminology - SOAP
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SOAP (Simple Object Access Protocol)
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A common way to package messages that are
exchanged between two processes.
A common set of serialization techniques for the data
that is exchanged.
A mechanism that allows Remote Procedure Calls
(RPC) to be made across a heterogeneous set of
platforms.
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Web Service Terminology – XSDL
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XSDL (XML Schema Definition Language)
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XSDL defines the layout of and the constraints on an
XML document.
XSDL supplants a previous standard known as Data
Type Definition (DTD).
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Web Service Terminology - UDDI
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UDDI (Universal Description, Discovery, and
Integration) registry
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The most commonly known method of discovering
Web services.
UDDI registry’s structure is similar to the phone book
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White page: list contact information and descriptions of
companies.
Yellow page: provide classification information about
companies and details on companies’ electronic capability.
Green page: list technical data regarding services.
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Web Service Terminology - WSDL
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WSDL (Web Service Description Language)
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It provides details about the functionality that is
implemented, which messages are used to request the
service, and the sequence in which the messages are
exchanged.
It is XML-based format.
Similar to the documentation to the ActiveX
components.
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Web Service Terminology - others
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XML ( eXtended Markup Language)
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GXA (Global XML Architecture)
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The main language used in Web service.
A set of protocols defined by Microsoft and others.
It provides an infrastructure that supports the most
commonly requested demands for commercial Web
service: security and routing.
WS-Security
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It allows authentication established by one system to be
accepted by others (federated identity).
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Web Service Terminology - others
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WS-Routing
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The typical mode for WS-Routing is to create a oneway path that the SOAP message must take.
WS-Referral
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A protocol directly related to WS-Routing.
It allows for changes to the routing of a SOAP message
to be made dynamically.
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Delivering Web Service
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Service-oriented Architecture
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Created by IBM.
Service provider
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A server or system makes a Web service available over
network.
Provides a service interface, that enables other applications to
access the service.
Service broker
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Service provider publishes its service to service broker.
Service broker communicates with requesters and directs them
to the appropriate provider.
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Delivering Web Service
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Service requester
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A networked server or system that access or employed a Web
service.
Service
provider
bind
publish
Service
broker
find
Service
requester
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Web Service Life-cycle Stages
Creation
Design, development, documentation, testing
and distribution.
Publication
Web service hosting and maintenance.
Promotion
Directory services, value-added services and
accreditation.
Sale
Auditing and accounts management.
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ASP .Net Web Service Architecture
VB
Application
Browser
Office
Documents
Other Web
Service
SOAP Messages
Classic ASP
ASP .Net
XML Web
Services
.ASP
.ASPX
.ASMX
RPC-Style
Listener
WSDL
Document-Style
Listener
WSDL
Wrapper Classes
Business
Objects
Database
Server
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