Web Services Description Language describes operations that ran be onvoked on the service. The operations are typically bunched into logical groups. The operations should be thought of as methods. The logical groups should be thought of as classes.

• defines the data types needed to interact with the service
• describes a service's i/o parameters
• method signatures of operations
• logically group the operations
• protocol used to access the service
• the specific address of the service
  WSDL documents describing useful services are pretty complicated. That is, anything much more complicated than 'Hello World' or the ubiquitous 'Stock Quote' examples is difficult to read but the basic structure looks like this.