What's the difference between and in WSDL?

Question

Both and seem to define an operation and its message. I don\'t quite understand, why are they both necessary?

Answer 1

Interfaces (wsdl:portType)

The WSDL portType element defines a group of operations (sometimes known as an interface).

The operation elements contain a combination of input and output elements. There can be a fault element when you have an output element. The order of these elements defines the message exchange pattern (MEP) (One-way, Request – Response, etc)

wsdl:binding

The WSDL binding element describes the concrete details of using a particular portType with a given protocol.