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This article will move through basics of Web Services, the various Web Services platform elements SOAP (Simple Object Access Protocol), UDDI (Universal Description, Discovery and Integration) and WSDL (Web Services Description Language).
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What is Web Services?
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Web Services is a platform to build loosely coupled applications.
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- Microsoft's DCOM (Distributed Component Object Model) for communication between networked computers access remote COM (Component Object Model) interface through remote procedure calls.
- Corba uses IIOP (Internet Inter-ORB Protocol) to access remote objects.
- In Java RMI (Remote Method Invocation) is used to access an EJB (Enterprise Java Bean) object which is again language specific.
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The typical syntax of a WSDL document is shown in the following example.
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The syntax of a WSDL suggests that it is a set of definitions where the definition element is at the root.
Let us try to understand each element in a WSDL document using a HelloWorld.wsdl document. This WSDL document is automatically generated by the Geronimo Eclipse Plugin (GEP). With the tutorials listed at the end of this document you will learn how to generate it using Eclipse and GEP.
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- <types>
Web Service is all about sending and receiving messages. The <types> element describes the various messages which will be used by the service. Basically it defines the various data types. As can be seen, HelloWorld service uses hello and helloResponse as the two messages.
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- <service>
Service element defines where the service can be accessed. Each service is associated with a unique name which is suggested by <wsdl:service name="HelloWorldService"> in our example. The next element <wsdl:port binding="intf:HelloWorldSoapBinding" name="HelloWorld"> suggests the previous binding which will be used by service. The element <wsdlsoap:address location="http://localhost:8080/SimpleWeb/services/HelloWorld"/> suggests the physical address through which a service can be accessed.
Web Services tutorials
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