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An Introduction to Web Services

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Title: An Introduction to Web Services


1
An Introduction to Web Services
2
Outline
  • What is a Web service
  • Background
  • Standards
  • XML XML Namespaces, XML Schema,WSDL, SOAP
  • Tools APIs
  • DOM/SAX,JAX-RPC/JAX-M
  • Apache SOAP/Axis, MS .NET, Python, C, C
  • Run time Environments
  • App Server/Web Server/Servlet, Client/Server,
    Standalone/Embedded

3
What is a Web service?
  • A service on the Web?
  • An IBM MS Collaboration?
  • SOAP? HTTP? XML?
  • W3C A Web service is a software system
    identified by a URI RFC 2396, whose public
    interfaces and bindings are defined and described
    using XML. Its definition can be discovered by
    other software systems. These systems may then
    interact with the Web service in a manner
    prescribed by its definition, using XML based
    messages conveyed by Internet protocols.

4
Background
  • HTTP GETs, POSTs
  • HTML no good interface for machines
  • Code Reuse, Component Reuse, Service Reuse
  • IBM and MS with separate Specifications. Joined
    forces under W3C umbrella
  • WSDL, SOAP, BPEL4WS

5
Standards XML XML Namespaces
  • Well Formed vs Valid
  • Well Formed Bracket matches, single document
    element
  • Valid complies to XML Schema or DTD
  • Namespaces Globally unique Scoping based on
    URIs, Imports schema reuse
  • QName NamespaceURILocalName

6
Standards XML Schema
  • Schema definition language based on XML
  • Defined using its own constructs
  • Constructs simpleType, complexType
  • Types string, integer, float
  • Check out Primer http//www.w3.org/TR/xmlschema-0
    /

7
Standards WSDL
  • Web Service Description Language
  • Abstract Types, Message, Interface Definitions
  • Concrete Binding, Service Definitions
  • Endpoints URI where to send messages
  • SOAP/HTTP/XML Schema optional!

8
Standards SOAP
  • Simple Object Access Protocol
  • No Object refs, No state assumptions
  • Envelope, Headers (optional), Bodies (mandatory
    payload)
  • Message Exchange Patterns
  • Feature Markup/Roles
  • Document/Literal, RPC/Encoded
  • All WS- specs targeted towards SOAP (WS-Security,
    WS-Routing)

9
Tools APIs XML APIs
  • DOM/SAX
  • JAX- family RPC, M, R, P, B
  • www.jcp.org
  • J2EE, JAX-Pack

10
Tools APIs Apache SOAP, Axis
  • Apache SOAP First Open Source SOAP
    Implementation
  • Axis next generation Apache SOAP, New Code base
    lessons learned from Apache SOAP development,
    JAX-RPC compliant
  • GT3 based on Axis

11
Tools APIs Microsoft .NET
  • .NET Framework
  • WSDL, XML Schema tools, SOAP, WSDL, XML APIs
  • IIS, ASP.NET, Visual Studio
  • Web server, IDE, Web service Wizards
  • CLR, Visual Basic, C

12
Tools APIs Python, C, C
  • Python
  • SOAPpy
  • WSDL and SOAP support
  • C/C
  • gSOAP (SOAP, WSDL)
  • Apache Axis C

13
Run Time Environments
  • HTTP Web Server (Tomcat), SOAP Servlet (Axis)
  • Application Server (JBOSS, WebSphere, IIS)
  • Client side only toolkits, Client/Server
  • Standalone/Embedded

14
Further Reading
  • http//www.w3.org/TR/
  • http//www.webservices.org/
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