WSDL Tutorial – Introduction to WSDL

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WSDL Tutorial

The Web Services Description Language is an XML-based interface description language that is used for describing the functionality offered by a web service. A WSDL description of a web service (also referred to as a WSDL file) provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. It thus serves a purpose that corresponds roughly to that of a method signature in a programming language.

The current version of WSDL is WSDL 2.0. The meaning of the acronym has changed from version 1.1 where the D stood for Definition.


WSDL Abstract:

  • WSDL stands for Web Services Description Language
  • WSDL is an XML based protocol for information exchange in decentralized and distributed environments.
  • WSDL is the standard format for describing a web service.
  • WSDL definition describes how to access a web service and what operations it will perform.
  • WSDL is a language for describing how to interface with XML-based services.
  • WSDL is an integral part of UDDI, an XML-based worldwide business registry.
  • WSDL is the language that UDDI uses.
  • WSDL was developed jointly by Microsoft and IBM.
  • WSDL is pronounced as ‘wiz-dull‘ and spelled out as ‘W-S-D-L

Objects in WSDL 1.1 / WSDL 2.0

WSDL 1.1 Term WSDL 2.0 Term Description
Service Service Contains a set of system functions that have been exposed to the Web-based protocols.
Port Endpoint Defines the address or connection point to a Web service. It is typically represented by a simple HTTP URL string.
Binding Binding Specifies the interface and defines the SOAP binding style (RPC/Document) and transport (SOAP Protocol). The binding section also defines the operations.
PortType Interface Defines a Web service, the operations that can be performed, and the messages that are used to perform the operation.
Operation Operation Defines the SOAP actions and the way the message is encoded, for example, “literal.” An operation is like a method or function call in a traditional programming language.
Message n/a Typically, a message corresponds to an operation. The message contains the information needed to perform the operation. Each message is made up of one or more logical parts. Each part is associated with a message-typing attribute. The message name attribute provides a unique name among all messages. The part name attribute provides a unique name among all the parts of the enclosing message. Parts are a description of the logical content of a message. In RPC binding, a binding may reference the name of a part in order to specify binding-specific information about the part. A part may represent a parameter in the message; the bindings define the actual meaning of the part. Messages were removed in WSDL 2.0, in which XML schema types for defining bodies of inputs, outputs and faults are referred to simply and directly.
Types Types Describes the data. The XML Schema language (also known as XSD) is used (inline or referenced) for this purpose.


WSDL Usage:
WSDL is often used in combination with SOAP and XML Schema to provide web services over the Internet. A client program connecting to a web service can read the WSDL to determine what functions are available on the server. Any special data types used are embedded in the WSDL file in the form of XML Schema. The client can then use SOAP to actually call one of the functions listed in the WSDL.

History of WSDL
WSDL 1.1 was submitted as a W3C Note by Ariba, IBM and Microsoft for describing services for the W3C XML Activity on XML Protocols in March 2001.

WSDL 1.1 has not been endorsed by the World Wide Web Consortium (W3C), however it has just (May 11th, 2005) released a draft for version 2.0, that will be a recommendation (an official standard), and thus endorsed by the W3C.

The WSDL describes services as collections of network endpoints, or ports. The WSDL specifications provides an XML format for documents for this purpose. The abstract definitions of ports and messages are separated from their concrete use or instance, allowing the reuse of these definitions. A port is defined by associating a network address with a reusable binding, and a collection of ports defines a service. Messages are abstract descriptions of the data being exchanged, and port types are abstract collections of supported operations. The concrete protocol and data format specifications for a particular port type constitutes a reusable binding, where the operations and messages are then bound to a concrete network protocol and message format. In this way, WSDL describes the public interface to the Web service.

Table of Contents-
WSDL Introduction
This chapter explains what is WSDL and why to use WSDL.
WSDL Elements
This chapter gives introduction of WSDL elements.
WSDL Hello World Example
This chapter gives an example of WSDL document.
WSDL Definition
This chapter describes WSDL Definition element of the document.
WSDL Message
This chapter describes WSDL Message element of the document.
WSDL Port Type
This chapter describes WSDL portType element of the document.
WSDL Binding
This chapter describes WSDL Binding element of the document.
WSDL Ports
This chapter describes WSDL Port element of the document.
WSDL Service
This chapter describes WSDL Binding Service of the document.
WSDL Summary
This chapter contains a recommendation on what subject you should study after the WSDL tutorial.

1. Wikipedia for WSDL


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