A SOAP method is an HTTP request/response that complies with the SOAP encoding rules.
HTTP + XML = SOAP
A SOAP request could be an HTTP POST or an HTTP GET request.
SOAP stands for Simple Object Access Protocol
SOAP is a communication protocol
SOAP is for communication between applications
SOAP is a format for sending messages
SOAP is designed to communicate via Internet
SOAP is platform independent
SOAP is language independent
SOAP is based on XML
SOAP is simple and extensible
SOAP allows you to get around firewalls
SOAP will be developed as a W3C standard
Why SOAP?
It is important for application development to allow Internet communication between programs.
Today's applications communicate using Remote Procedure Calls (RPC) between objects like DCOM and CORBA, but HTTP was not designed for this. RPC represents a compatibility and security problem; firewalls and proxy servers will normally block this kind of traffic.
A better way to communicate between applications is over HTTP, because HTTP is supported by all Internet browsers and servers. SOAP was created to accomplish this.
SOAP provides a way to communicate between applications running on different operating systems, with different technologies and programming languages.
Soap relies on HTTP as a transport mechanism to send XML based messages, the messages are packed in what is called a SOAP envelop and send to the server to process in a Request/Response fashion. SOAP unlike proprietary protocols like DCOM or RMI does not require strong connection between client and the server and the SOAP messages are sting based messages passed from the Client to Server and vice versa in the form of SOAP envelops.
Syntax Rules
Here are some important syntax rules:
A SOAP message MUST be encoded using XML
A SOAP message MUST use the SOAP Envelope namespace
A SOAP message MUST use the SOAP Encoding namespace
A SOAP message must NOT contain a DTD reference
A SOAP message must NOT contain XML Processing Instructions
Skeleton SOAP Message
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
...
...
...
...
...
...
SOAP and Security
SOAP as it works on HTTP get the benefits of all the security that are currently available to HTTP, a SOAP message can pass through the firewall of the web server normally from port 80.
Limitations of SOAP Though SOAP is evolving, and has a number of striking features, which are important in development of, distributed applications but still there are certain things which SOAP cannot support which I would like to address
SOAP is a simple protocol: As the name suggests it's a simple protocol and works on HTTP, we cannot expect all the functionality's offered by other protocols like DCOM or RMI.
SOAP may turn out to be slower compared to other proprietary protocols as it requires additional XML processing.
Still SOAP fares well in most areas compared to other wire protocol. As per the specifications, SOAP can also use other transport carrier like SMTP to transmit SOAP messages. Still lot of information on this topic in not available.
