Service Oriented Architecture (SOA) Made Simple

Even if you're wrapping a legacy application, you'll need a service description that other web services applications can use. Of course, there are many data-binding tools available that are, for example, capable of turning a Java class into an XML Schema or a Windows-compatible wizard with a "generate WSDL" button. But even then, you'll have to give those descriptions to others, the tools may have bugs (surprising, I know, but it's been known to happen), or you'll need to hand-tweak the generated files because a particular customer "just wants the namespace or URL changed." At that point, you don't want to have to burn the midnight oil with a copy of the WSDL and Schema specs in hand and the generated WSDL file on your screen.

Salz, Rich. XML.com (2005). Articles>Information Design>XML