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A WSDL [1] document describes a Web service. It provides information that an
application client needs to connect and communicate with a service.
WSDL defines three things about a Web service. It defines what the service
does, how it communicates, and where to find it. The various parts of a Web
service description can be separated into multiple documents to provide more
flexibility and to increase reusability. These parts are as follows:
- The "what" part of a WSDL document, called a portType, defines the
abstract interface of the Web service. It specifies what operations the
service supports, and it defines the format of the messages that the
applications must exchange to perform each operation.
- The "how" part of a WSDL document, called a binding, maps an abstract
interface to a concrete set of protocols. The binding specifies the
technical details of how to communicate with a Web service. It indicates how
the input and output messages defined in the abstract interface should be
packaged into a message, and it specifies what communication protocols the
Web service supports. The binding also specifies how to pass system-level
information, such as security credentials or transaction identifiers, with
the message. A WSDL document may define multiple bindings for the same
abstract interface.
- The "where" part of a WSDL document, called a service, describes a
specific Web service implementation. A Web service implementation can
support one or more portTypes, each with one or more bindings. Each
implementation binding, called a port, specifies an endpoint, which is the
URL of the service. A business might offer multiple endpoints to a
particular service, each implementing a different binding to support
multiple protocols.
WSDL is the basis of most Web services development tools. WSDL is a
machine-readable description, which a developer can compile into a
communication routine, called a proxy. The proxy contains application code
that constructs the messages and manages the communication on behalf of the
client application. The proxy automatically maps the XML message structures
into native language objects that can be directly manipulated by the
application. The proxy frees the developer from having to understand and
manipulate XML.
[1] Web Services Description Language .
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