Using XML with WSDL

Service Oriented Architecture SOA - Using XML with WSDL

WSDL uses XML to define messages. XML has a tagged message format. This is shown in the above figure. The tag has the value of Burnsville. And is the ending tag indicating the end of the value of city. Both the service provider and service consumer use these tags. In fact, the service provider could send the data shown at the bottom of this figure in any order. The service consumer uses the tags and not the order of the data to get the data values. More on the use of XML tags and a comparison of XML to using fixed record formats can be found in chapter 3 of Web Services and Service-Oriented Architectures: The Savvy Manager's Guide.

Source: http://www.service-architecture.com/web-services/articles/web_services_explained.html