December 12, 2001 - Application-Specific Protocols
WSDL (Web Services Description Language) is used for two purposes. First, it is a documentation language for Web services. When calling a Web service, you need to know how many parameters are expected and of which type each parameter is. Secondly, it determines what gets on the Internet, for both the clients and the servers. The SOAP protocol uses low-level protocols such as IP and HTTP. The application determines the high-level protocol that it uses between a particular client and a particular server. The high-level protocol describes the count of parameters, the type of each parameter, and how those parameters are to be sent through the wire (serialization). WSDL is used to describe this protocol. Here is an example for a function call "foo(5131953)":
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SOAP-ENV:Envelope
SOAP-ENV:encodingStyle="https://schemas.xmlsoap.org/soap/encoding/"
xmlns:SOAP-ENV="https://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Body>
<m:foo xmlns:m="https://tempuri.org/message/">
<arg>5131953</arg>
</m:foo>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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