W E B   S E R V I C E S  

declared, referred, imported, and even inherited. They are then instantiated by particular 

tags in a document, such as properly structured elements and attributes.  

Example of XML Schema document   CGJ 

What is SOAP, WSDL and UDDI? 

The Simple Object Access Protocol (SOAP) is an RPC protocol that uses XML as the 

encoding language and that uses standard internet protocols, such as HTTP and SMTP as 

the transport medium.  

Example of SOAP message   CGJ 

For SOAP, there exists also corresponding meta language that is called Web Service 

Description Language (WSDL). WSDL has a similar function than the Interface Definition 

Language has in Corba. It describes service interfaces (port types) in terms of the operations 

(request messages and response messages) that can be invoked. It describes particular 

service instances by binding a port type to a particular transport endpoint. 

Example of WSDL description   CGJ 

The Universal Description Discovery Integration (UDDI) is a  standardized interface to Web 

Service registries   a kind of global and platform neutral version of JNDI in which WSDL 

descriptions are hosted and can be searched. UDDI registries are themselves Web Services 

in that they support the SOAP protocol. 

What are JAXM, JAX RPC & JAXR?  

We can distinguish two modes of XML/SOAP messaging. The simplest, but very 

unconvenient mode is to interact with the XML/DOM documents representing method 

requests and responses immediately. It is suitable for untyped applications or special 

purpose logic that is based on XML processing anyway. There is an API under development, 

JAXM (Java Api for XML Messaging), which will support this mode. 

Whenever we are not primarily interested in manipulating XML and have a strongly typed 

environment, such as in J2EE  logic, we need a more elaborated mode that is an extension 

to Remote Method Invocation (RMI). The corresponding extension API to the Java2  

platform is called JAX RPC. In JAX RPC, an XML message is processed through a chain of 

so called handlers before it is (de )serialized into/from Java objects using a set of so called 

type mappings.  

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