How does a WSDL

WSDL tutorial: Web Service Description Language explained

When working with web services, various techniques play a major role. In addition to SOAP and REST, this is primarily the description language WSDL. This describes the functions of a web service so that other network participants can also use the services. How does the language work, what exactly do you need the WSDL file for and what connections are there to other languages?

What does WSDL mean?

WSDL stands for Web Service Description Language. It is therefore a metalanguage with which web services can be comprehensively described. A web service, in turn, is a service that a server makes available to clients via the Internet (or another network). This works independently of the platform - i.e. between a wide variety of systems and applications. A WSDL file is available on the server so that a client can find out about the possibilities and procedures of the web service. From the details conveyed in the file, the client knows how to call the web service.

WSDL builds on the Extensible Markup Language (XML) or the XML schema (XSD). That means: XML elements are used in WSDL.

WSDL is standardized by the World Wide Web Consortium (W3C).

Structure and properties of WSDL

WSDL is used to describe web services abstract and concrete descriptions. While the abstract description relates to the functional scope of the service, the concrete description provides clear facts such as the transmission protocol. The document (i.e. the WSDL file) has a hierarchical structure. Information is therefore shown nested.

WSDL takes six main elements from XML:

  • types: Data types
  • messages: Description of the data to be transferred
  • interface: abstract operations that describe the communication between server and client (was called in an older version of the standard portType)
  • binding: Information about the transport protocol used
  • endpoint: Information about the communication interface, usually in the form of a URI (was called in an older version of the standard port)
  • service: Access points of the web service

If you fill in all the elements in the file, the client receives all the information it needs to use the web service. This is precisely why a web service is platform-independent, because the different systems receive the common language through the WSDL file.

WSDL example

We will now take a closer look at the structure of a WSDL file using an example. The following code is intended for a web service that returns a simple "Hello World".

 

In the source code example you can see the individual components of a WSDL file. After an initial introduction, which also contains a reference to WSDL and XSD, the abstract descriptions follow types, messages and interface. The second half finally consists of the concrete descriptions, whereby endpoint in service is incorporated.

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