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Ø Web Services Description Language (WSDL)
Ø Web Services Description Language (WSDL) is a format for describing a Web Services interface. It is a way to describe services and how they should be bound to specific network addresses. WSDL has three parts:
ü Service bindings
Ø Definitions are generally expressed in XML and include both data type definitions and message definitions that use the data type definitions.
Ø These definitions are usually based upon some agreed upon XML vocabulary. This agreement could be within an organization or between organizations.
Ø Vocabularies within an organization could be designed specifically for that organization. They may or may not be based on some industry-wide vocabulary.
Ø If data type and message definitions need to be used between organizations, then most likely an industry-wide vocabulary will be used.
Ø XML, however, is not necessary required for definitions. The OMG Interface Definition Language (IDL), for example, could be used instead of XML.
Ø If a different definitional format were used, senders and receivers would need to agree on the format as well as the vocabulary. Nevertheless, over time, XML-based vocabularies and messages are likely to dominate.
Ø XML Namespaces are used to ensure uniqueness of the XML element names in the definitions, operations, and service bindings.
Ø Operations describe actions for the messages supported by a Web service. There are four types of operations:
ü One-way: Messages sent without a reply required
ü Request/response: The sender sends a message and the received sends a reply.
ü Solicit response: A request for a response. (The specific definition for this action is pending.)
ü Notification: Messages sent to multiple receivers. (The specific definition for this action is pending.)
Ø Operations are grouped into port types. Port types define a set of operations supported by the Web service.
Ø Service bindings connect port types to a port. A port is defined by associating a network address with a port type. A collection of ports defines a service. This binding is commonly created using SOAP, but other forms may be used. These other forms could include CORBA Internet Inter-ORB Protocol (IIOP), DCOM, .NET, Java Message
Service (JMS), or WebSphere MQ to name a few.
The following figure shows the relationship of the basic parts of WSDL:
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