Microsoft SOAP: Simple Object Access Protocol

The Simple Object Access Protocol (SOAP) is a lightweight and simple XML-based protocol that is designed to exchange structured and typed information on the Web. SOAP can be used in combination with a variety of existing Internet protocols and formats including Hypertext Transfer Protocol (HTTP), Simple Mail Transfer Protocol (SMTP), and Multipurpose Internet Mail Extensions (MIME), and can support a wide range of applications from messaging systems to remote procedure calls (RPCs).

SOAP consists of three parts:

• The SOAP envelope construct defines an overall framework for expressing whatis in a message; who should deal with it, and whether it is optional or mandatory.
• The SOAP encoding rules defines a serialization mechanism that can be used to exchange instances of application-defined datatypes.
• The SOAP RPC representation defines a convention that can be used to represent remote procedure calls and responses.

SOAP messages are basically one-way transmissions from a sender to a receiver, but SOAP messages are often combined to implement patterns such as request/response. All SOAP messages are encoded using XML, which is an XML document that consists of a mandatory SOAP envelope, an optional SOAP header, and a mandatory SOAP body.

Binding SOAP to HTTP provides the advantage of being able to use the formalism and decentralized flexibility of SOAP with the rich feature set of HTTP. Carrying SOAP in HTTP does not mean that SOAP overrides existing semantics of HTTP but rather that the semantics of SOAP over HTTP maps naturally to HTTP semantics. In the case of using HTTP as the protocol binding, an RPC call maps naturally to an HTTP request and an RPC response maps to an HTTP response. However, using SOAP for RPC is not limited to the HTTP protocol binding.

SOAP message format:

SOAP header

<SOAP-ENV: Envelope

Attributes>

<SOAP-ENV:Boby

Attributes

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Example 1 SOAP Message Embedded in HTTP Request

POST /StockQuote HTTP/1.1
Host: www.stockquoteserver.com
Content-Type: text/xml; charset="utf-8"
Content-Length: nnnn
SOAPAction: "Some-URI"

<SOAP-ENV:Envelope
  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
  SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body>
 <m:GetLastTradePrice xmlns:m="Some-URI">
  <symbol>DIS</symbol>
 </m:GetLastTradePrice>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Following is the response message containing the HTTP message with the SOAP message as the payload:

Example 2 SOAP Message Embedded in HTTP Response

HTTP/1.1 200 OK
Content-Type: text/xml; charset="utf-8"
Content-Length: nnnn

<SOAP-ENV:Envelope
  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
  SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
<SOAP-ENV:Body>
 <m:GetLastTradePriceResponse xmlns:m="Some-URI">
  <Price>34.5</Price>
 </m:GetLastTradePriceResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>    

Related Protocols
HTTP , MIME , SMTP , RCP, XML

Sponsor Source

SOAP is defined by Microsoft.

Reference
http://www.w3.org/TR/2000/NOTE-SOAP-20000508/ : Simple Object Access Protocol (SOAP)