Oracle?..hunm..I am pretty sure most of the XML used in XML is for configurational purposes,such as how oracle may behave in a certain situation?,,,,they may keep this behavior description in XML files etc.
Webservices is a pretty neat idea.As we all know that developers have always been bummed by the fact that they have to write applications system/OS specific (heck we have to write browser specific code..darn).
When Java was introduced,it was the main promotional slogan for it
"Write once use everywhere"
There may be arguments that wether java has fullfilled the task or not,but it seems like webservices is definitley is up to the task.
A corporation or a person will write an application and then werite a Webservice for it,this will define what parts of application may be accesed by any one from any OS using SOAP messages.
There are already standards around that complement XML to create standard description files.
Essentially what hapens is that if I have an application on windows machine and I want it to be available for a linux user,I will create webservice using
WSDL - Web Services Definition Language
SOAP - Simple Object Access Protocol
In this service's description I will define what are the parts of my application that can be accessed by any one sending a message(SOAP) over the HTTP(typically).
Below is the Official description by W3C
[Definition: A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP-messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.]
I hope it was usefull description...I tried..