WSDL TUTORIAL
WSDL (Web Services Description Language) is an XML-based language for describing Web services and how to access them.
WSDL is an XML-based language for describing Web services and how to access them.
What You Should Already Know
Before you continue you should have a basic understanding of the following:
- XML
- XML Namespaces
- XML Schema
If you want to study these subjects first, find the tutorials on our Home page.
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 Describes Web Services
WSDL stands for Web Services Description Language.
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.
WSDL is a W3C Recommendation
WSDL became a W3C Recommendation 26. June 2007.
You can read more about the XML Schema standard in our W3C tutorial.
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 |
| | The operations performed by the web service |
| | The messages used by the web service |
| | The data types used by the web service |
| | The communication protocols used by the web service |
The main structure of a WSDL document looks like this:
| definition of types........
definition of a message....
definition of a port.......
definition of a binding....
|
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.
For a complete syntax overview go to the chapter WSDL Syntax.
WSDL Ports
The
It describes a web service, the operations that can be performed, and the messages that are involved.
The
WSDL Messages
The
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
For maximum platform neutrality, WSDL uses XML Schema syntax to define data types.
WSDL Bindings
The
WSDL Example
This is a simplified fraction of a WSDL document:
|
|
In this example the
The "getTerm" operation has an input message called "getTermRequest" and an output message called "getTermResponse".
The
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.
WSDL Ports
The
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
A one-way operation example:
|
|
In this example 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
A request-response operation example:
|
|
WSDL Bindings
Binding to SOAP
A request-response operation example:
|
transport="http://schemas.xmlsoap.org/soap/http" /> soapAction="http://example.com/getTerm"/>
|
The binding element has two attributes - the name attribute and the type attribute.
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 - the style attribute and the transport attribute.
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".
In this example 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 and UDDI
Universal Description, Discovery and Integration (UDDI) is a directory service where businesses can register and search for Web services.
What is UDDI
UDDI is a platform-independent framework for describing services, discovering businesses, and integrating business services by using the Internet.
- UDDI stands for Universal Description, Discovery and Integration
- UDDI is a directory for storing information about web services
- UDDI is a directory of web service interfaces described by WSDL
- UDDI communicates via SOAP
- UDDI is built into the Microsoft .NET platform
What is UDDI Based On?
UDDI uses World Wide Web Consortium (W3C) and Internet Engineering Task Force (IETF) Internet standards such as XML, HTTP, and DNS protocols.
UDDI uses WSDL to describe interfaces to web services
Additionally, cross platform programming features are addressed by adopting SOAP, known as XML Protocol messaging specifications found at the W3C Web site.
UDDI Benefits
Any industry or businesses of all sizes can benefit from UDDI
Before UDDI, there was no Internet standard for businesses to reach their customers and partners with information about their products and services. Nor was there a method of how to integrate into each other's systems and processes.
Problems the UDDI specification can help to solve:
- Making it possible to discover the right business from the millions currently online
- Defining how to enable commerce once the preferred business is discovered
- Reaching new customers and increasing access to current customers
- Expanding offerings and extending market reach
- Solving customer-driven need to remove barriers to allow for rapid participation in the global Internet economy
- Describing services and business processes programmatically in a single, open, and secure environment
How can UDDI be Used
If the industry published an UDDI standard for flight rate checking and reservation, airlines could register their services into an UDDI directory. Travel agencies could then search the UDDI directory to find the airline's reservation interface. When the interface is found, the travel agency can communicate with the service immediately because it uses a well-defined reservation interface.
Who is Supporting UDDI?
UDDI is a cross-industry effort driven by all major platform and software providers like Dell, Fujitsu, HP, Hitachi, IBM, Intel, Microsoft, Oracle, SAP, and Sun, as well as a large community of marketplace operators, and e-business leaders.
Over 220 companies are members of the UDDI community.
The Full WSDL Syntax
The full WSDL 1.2 syntax as described in the W3C Working Draft is listed below.
<-- binding details --> *
<-- binding details --> *
<-- binding details -->
<-- binding details --> *
<-- binding details --> *
<-- address details -->
You Have Learned WSDL, Now What?
WSDL Summary
This tutorial has taught you how to create WSDL documents that describes a web service. It also specifies the location of the service and the operations (or methods) the service exposes.
You have learned how to define the message format and protocol details for a web service.
You have also learned that you can register and search for web services with UDDI.
Now You Know WSDL, What's Next?
The next step is to learn about SOAP and Web Services.
SOAP
SOAP is a simple XML-based protocol that allows applications to exchange information over HTTP.
Or more simply: SOAP is a protocol for accessing a web service.
If you want to learn more about SOAP, please visit our SOAP tutorial.
Web Services
Web services can convert your applications into web-applications.
By using XML, messages can be sent between applications.
If you want to learn more about web services, please visit our Web Services tutorial.
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