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.”[RFC 2396]

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 = NamespaceURI:LocalName

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:

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 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