http://www.sajim.co.za/news.main.3nr1.asp?print=1


   
  News Vol.3(1) June 2001

An Overview of WSDL 
Margaret van Steenderen 
Margaret.vansteenderen@commercequest.co.za 

Pierre van Dyk 
pvandyk@global.co.za 

With XML still catching on like wildfire, now is the exciting time as applications, services 
and protocols are built using XML as the foundation. This column provides an overview of 
the Web Services Description Language (WSDL). 

Introduction 

WSDL is a specification that is part of the UDDI initiative. A very brief recap of UDDI: 

It provides a business registry, enabling businesses to find each other through 
supplying: 

General Business Information  
Business Categories  
Business rules enabling business transactions  

What is needed on a technical level for business interaction  

The last point, what is needed on a technical level, is where WSDL comes in. 

What is WSDL? 

According to Microsoft, 'WSDL is an XML format for describing network services as a set 
of endpoints operating on messages containing either document-oriented or procedure-
oriented information'. Just like it’s name, Web Services Description Language, WSDL is 
used to describe. Service providers can describe the basic format of requests to their systems 
using WSDL. This is done through WSDL having three components, these are: 

1. Message. Defines the format of the messages, described in a neutral way.  This means 
that the client and server do not need to be running similar databases, or databases 
that are compatible in some way with each other, it is the actual message that is 
important. It describes what data in the form of messages is required to do business. It 
then describes what possible return messages there will be. It may describe an error 
message format should this be applicable.   

2. Binding. This is the communication information that is required, that is, the types of 
transport protocols, for example, SOAP transported over HTTP.  

3. Service. The service ties the messages to the binding. This is because there could be 
multiple messages that require different types of communication layers. It also 
provides the location of the service, for example, a specific Internet address.  

Example 



The following is a reduced example of WSDL that queries and provides a reply about a 
person’s credit rating using their South African identity number. The pre-emptory name 
space definitions have been left out. 

<message name="CreditRatingRequest"> 

  <part  name="IdentityNumber" type="xsd:string"/> 

</message> 

<message name="CreditRatingResponse"> 

  <part  name="RatingDescription" type="xsd:string"/> 

</message> 

The message format here describes that an Identity Number is needed in a string format and 
that a credit rating description will be returned, also in a string format 

<binding name="CreditRatingBinding" type="CreditRating"> 

  <soap:binding style="rpc" 

                transport="http://schemas.xmlsoap.org/soap/http"/> 

  <operation name="start"> 

    <soap:operation soapAction="urn:CreditRating"/> 

    <input> 

      <soap:body 

          encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" 

          namespace="urn:CreditRating" 

          use="encoded"/> 

    </input> 

    <output> 

<!-- This contains the same information as the input section --> 

    </output> 

  </operation> 

</binding> 

The binding information above describes the communications protocol to use, namely 
SOAP over HTTP. 



<service name="CreditRating"> 

  <documentation>example.com CreditRating service</documentation> 

  <port binding="CreditRatingBinding" name="CreditRatingPort"> 

    <soap:address location="http://localhost:8080/soap/servlet/rpcrouter"/> 

  </port> 

</service> 

The above describes the location as well as providing a description of the service. 

Business benefits 

WSDL describes a company’s web services so that companies that wish to do business can 
easily see what is needed in order to do business. WSDL does not prescribe to the client 
what needs to be run, and the client does not need to know exactly what the server is 
running, so the applications is loosely coupled. 

So, WSDL is designed to be platform and language independent, it defines interfaces and 
describes the service to allow data interaction. UDDI enables companies to not only find 
each other, but through WSDL allows companies to initiate transactions without a lot of 
interaction between technical staff and potentially between previously incompatible 
systems. 

Conclusion 

The news columns have been presenting overviews of XML, SOAP, UDDI and now 
WSDL. These tie together to produce a powerful new tool for the modern enterprise called 
web services.  A web service allows companies to build loosely coupled distributed 
applications with clearly defined interfaces. See web services as the bricks and mortar for 
the world of distributed computing. 

Useful Web sites 

http://www.w3.org/TR/wsdl or http://msdn.microsoft.com/xml/general/wsdl.asp - the 
WSDL standards (these two sites are the same, use whichever is easier to load) 

http://www-106.ibm.com/developerworks/library/ws-soap/?loc=wstheme - ties WSDL and 
SOAP together 

http://www.alphaworks.ibm.com/ - provides toolkits, such as a WSDL toolkit and a Web 
Services toolkit 

http://xml.coverpages.org/wsdl.html - gives a history and general information on WSDL 

  

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ISSN 1560-683X

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