Wednesday, 1 June 2011

WSDL


WSDL is an XML-based language for describing Web services and how to access them.
WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes.

What is WSDL?

  • WSDL stands for Web Services Description Language
  • WSDL is written in XML
  • WSDL is an XML document
  • WSDL is used to describe Web services
  • WSDL is also used to locate Web services
  • WSDL is a W3C recommendation

 

WSDL Documents

A WSDL document is just a simple XML document. It contains set of definitions to describe a web service.

 

The WSDL Document Structure

A WSDL document describes a web service using these major elements:
Element
Defines
<types>
The data types used by the web service
<message>
The messages used by the web service
<portType>
The operations performed by the web service
<binding>
The communication protocols used by the web service

The main structure of a WSDL document looks like this:

<definitions>
<types>
  definition of types........
</types>
<message>
  definition of a message....
</message>

<portType>
  definition of a port.......
</portType>
<binding>
  definition of a binding....
</binding>
</definitions>

A WSDL document can also contain other elements, like extension elements, and a service element that makes it possible to group together the definitions of several web services in one single WSDL document.

 

WSDL Ports:

The <portType> element is the most important WSDL element.
It describes a web service, the operations that can be performed, and the messages that are involved.
The <portType> element can be compared to a function library (or a module, or a class) in a traditional programming language.

 

WSDL Messages

The <message> element defines the data elements of an operation.
Each message can consist of one or more parts. The parts can be compared to the parameters of a function call in a traditional programming language.

 

WSDL Types

The <types> element defines the data types that are used by the web service.
For maximum platform neutrality, WSDL uses XML Schema syntax to define data types.

 

WSDL Bindings

The <binding> element defines the message format and protocol details for each port.

 

Ex:

                   <message name="getTermRequest">
  <part name="term" type="xs:string"/>
</message>

<message name="getTermResponse">
  <part name="value" type="xs:string"/>
</message>

<portType name="glossaryTerms">
  <operation name="getTerm">
    <input message="getTermRequest"/>
    <output message="getTermResponse"/>
  </operation>
</portType>

In this example the <portType> element defines "glossaryTerms" as the name of a port, and "getTerm" as the name of an operation.
The "getTerm" operation has an input message called "getTermRequest" and an output message called "getTermResponse".
The <message> elements define the parts of each message and the associated data types.
Compared to traditional programming, glossaryTerms is a function library, "getTerm" is a function with "getTermRequest" as the input parameter, and getTermResponse as the return parameter.

WSDL Ports

A WSDL port describes the interfaces (legal operations) exposed by a web service.
The <portType> element is the most important WSDL element.
It defines a web service, the operations that can be performed, and the messages that are involved.
The port defines the connection point to a web service. It can be compared to a function library (or a module, or a class) in a traditional programming language. Each operation can be compared to a function in a traditional programming language.

Operation Types

The request-response type is the most common operation type, but WSDL defines four types:
Type
Definition
One-way
The operation can receive a message but will not return a response
Request-response
The operation can receive a request and will return a response
Solicit-response
The operation can send a request and will wait for a response
Notification
The operation can send a message but will not wait for a response

One-Way Operation:

<message name="newTermValues">
  <part name="term" type="xs:string"/>
  <part name="value" type="xs:string"/>
</message>

<portType name="glossaryTerms">
  <operation name="setTerm">
    <input name="newTerm" message="newTermValues"/>
  </operation>
</portType >
In the example above, the port "glossaryTerms" defines a one-way operation called "setTerm".
The "setTerm" operation allows input of new glossary terms messages using a "newTermValues" message with the input parameters "term" and "value". However, no output is defined for the operation.

 

Request-Response Operation:

<message name="getTermRequest">
  <part name="term" type="xs:string"/>
</message>

<message name="getTermResponse">
  <part name="value" type="xs:string"/>
</message>

<portType name="glossaryTerms">
  <operation name="getTerm">
    <input message="getTermRequest"/>
    <output message="getTermResponse"/>
  </operation>
</portType>

In the example above, the port "glossaryTerms" defines a request-response operation called "getTerm".
The "getTerm" operation requires an input message called "getTermRequest" with a parameter called "term", and will return an output message called "getTermResponse" with a parameter called "value".

 

 

WSDL Binding to SOAP

WSDL bindings defines the message format and protocol details for a web service.

<message name="getTermRequest">
  <part name="term" type="xs:string"/>
</message>

<message name="getTermResponse">
  <part name="value" type="xs:string"/>
</message>

<portType name="glossaryTerms">
  <operation name="getTerm">
    <input message="getTermRequest"/>
    <output message="getTermResponse"/>
  </operation>
</portType>

<binding type="glossaryTerms" name="b1">
   <soap:binding style="document"
   transport="http://schemas.xmlsoap.org/soap/http" />
   <operation>
     <soap:operation soapAction="http://example.com/getTerm"/>
     <input><soap:body use="literal"/></input>
     <output><soap:body use="literal"/></output>
  </operation>
</binding>

The binding element has two attributes - name and type.
The name attribute (you can use any name you want) defines the name of the binding, and the type attribute points to the port for the binding, in this case the "glossaryTerms" port.
The soap:binding element has two attributes - style and transport.
The style attribute can be "rpc" or "document". In this case we use document. The transport attribute defines the SOAP protocol to use. In this case we use HTTP.
The operation element defines each operation that the port exposes.
For each operation the corresponding SOAP action has to be defined. You must also specify how the input and output are encoded. In this case we use "literal".

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