Web Services Description Language
WSDL
WSDL stands for Web Services Description Language.
A WSDL document is written in XML, and it describes a web service: what it can do and how to talk to it.
Think of it as the menu and instruction manual for a web service.
What a WSDL file tells you:
- What the service can do (for example GetWeather or GetPrice)
- What to send (like a city name or product ID)
- What to get back (like a temperature or price)
- Where the service lives (its web address)
- How to send messages (almost always with SOAP over HTTP)
The main structure of a WSDL document looks like this:
<definitions>
<types>
what the data looks like (data type definitions)
</types>
<message>
what is sent and received....
</message>
<portType>
what the service can do......
</portType>
<binding>
how to send the messages (SOAP over HTTP)
</binding>
<service>
where the service lives....
</service>
</definitions>
The five parts:
| Part | What it answers |
|---|---|
| <types> | What does the data look like? |
| <message> | What goes in and out? |
| <portType> | What can the service do? |
| <binding> | How do I send messages |
| <service> | Where is it? |
WSDL Example
This is a simplified fraction of a WSDL document:
<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.
The <portType> Element
The <portType> element defines a web service, the operations that can be performed, and the messages that are involved.
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 |
WSDL One-Way Operation
A one-way operation example:
<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 portType "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.
WSDL Request-Response Operation
A request-response operation example:
<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 portType "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.
A request-response operation example:
<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 portType 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".
