What's the difference between <binding> and <portType> in WSDL?

Question

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

Answer 1

portType (Analogs to Java interface)

• PortType is an abstraction part of WSDL.
• An abstract set of operations supported by one or more endpoints.

binding

• Binding is an concrete part of WSDL.
• Describes how the operation is invoked by specifying concrete protocol and data format specifications for the operations and messages.

• bindings are three types

  1. SOAP Binding:
     SOAP binding allows either document or rpc style with either encoding or literal. Encoding indicates how a data value should be encoded in an XML format (These rules specify how "something" is encoded/serialized to XML and then later decoded/de-serialized from XML back to "something"). Literal means that the data is serialized according to a schema (this is just plain XML data). With transportation type http, jms, smtp...

  2. HTTP GET & POST binding:
     WSDL includes a binding for HTTP 1.1's GET and POST verbs in order to describe the interaction between a Web Browser and a web site.

  3. MIME binding: WSDL includes a way to bind abstract types to concrete messages in some MIME format.

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In WSDL 2.0 :

• PortTypes renamed to interfaces
• Ports renamed to endpoints
• Removed message constructs

Source

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Useful links

• WSDL Reading, a Beginner's Guide
• W3C: Web Services Description Language (WSDL) 1.1
• W3C: Simple Object Access Protocol (SOAP) 1.1