SOAP
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Simple Object Access Protocol (SOAP) is a protocol to exchange information or message using XML. It follows XML standard such as schema to define message in a structured way. Specifically, XML uses the WSDL (Web Services Description Language), a standard used for XML-based services on the web.
It still uses HTTP as the transport protocol over the network. When SOAP messages are transmitted over HTTP, they are typically encapsulated within the payload of an HTTP request (POST) or response. The HTTP headers and body are used to transport the SOAP message between the client and the server.
Here is an example of SOAP request encapsulated in HTTP POST method:
POST /exampleWebService HTTP/1.1
Host: www.example.com
Content-Type: application/soap+xml; charset=utf-8
Content-Length: [length]
<?xml version="1.0" encoding="UTF-8"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope/">
<soap:Header>
<!-- Optional header -->
</soap:Header>
<soap:Body>
<getWeather xmlns="http://example.com/weather/">
<city>New York</city>
</getWeather>
</soap:Body>
</soap:Envelope>
Request is sent to the /exampleWebService endpoint on the www.example.com server encapsulated in POST method. The content type specified is in SOAP XML format.
The soap:Envelope is the root element of a SOAP message, it defines the namespace with the soap envelope URI. The header contains optional information. The body specifies the actual SOAP message. The SOAP message here is using the <getWeather> operation with the New York City as the parameter.