As communications protocols
and message formats are standardized in the
web community, it becomes
increasingly possible and important to be able to describe the communications
in some structured way.WSDL addresses this need by defining an XML grammar for
describing network services as collections
of communication endpoints capable of
exchanging messages.
WSDL service definitions provide
documentation for distributed systems
and serve as a recipe for automating the details involved in applications
communication
A WSDL document defines
services as collections of network endpoints, or ports. In WSDL, the abstract
definition of endpoints and messages is separated from their concrete network
deployment or data format bindings. This allows the reuse of abstract
definitions: messages, which are abstract descriptions of the data being
exchanged, and port types which are abstract collections of operations. The
concrete protocol and data format specifications for a particular port type
constitutes a reusable binding. A port is defined by associating a network
address with a reusable binding, and a collection of ports define a service.
Hence, a WSDL document uses the following elements in the definition of network
services:
• Types– a container for data type
definitions using some type system (such as XSD).
• Message– an abstract, typed
definition of the data being communicated.
• Operation– an abstract description of
an action supported by the service.
• Port Type–an abstract set of
operations supported by one or more endpoints.
• Binding– a concrete protocol and data
format specification for a particular port type.
• Port– a single endpoint defined as a
combination of a binding and a network address.
• Service– a collection of related
endpoints.
It is important to observe that
WSDL does not introduce a new type definition language. WSDL recognizes the need for rich type
systems for describing message formats, and supports the XML Schemas
specification (XSD) [11] as its canonical type system. However, since it is
unreasonable to expect a single type system grammar to be used to describe all
message formats present and future, WSDL allows using other type definition
languages via extensibility.
In addition, WSDL defines a common
binding mechanism. This is used to attach a specific protocol or data format or
structure to an abstract message, operation, or endpoint. It allows the reuse
of abstract definitions.
In addition to the core service
definition framework, this specification introduces specific binding extensions
for the following protocols and message formats:
• SOAP 1.1
• HTTP GET / POST
• MIME
Structure Of A WSDL Document
<definitions>
<types>
definition
of types........
</types>
<message>
definition
of a message....
</message>
<portType>
definition
of a port.......
</portType>
<binding>
definition of a binding....
</binding>
</definitions>
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