SOAP stands for “Simple Object Access Protocol” and it’s a method of transferring messages, or small amounts of data, via the Internet. It uses the XML format and messages are usually sent via HTTP (hypertext transfer protocol). Both types of data transmission standards are widely supported. HTTP avoids most network firewalls (which is useful given that it’s the protocol that Web pages rely on) because firewalls don’t normally block port 80 (HTTP) traffic, so most SOAP messages won’t be hindered.
An “envelope” that features a header and a body encapsulates each SOAP message. The header can include the message ID and the date of sending, while the actual message is featured in the body. SOAP messages all use the same format, so they’re compatible with a wide variety of protocols and operating systems. This means that a user could send a SOAP message from a Windows XP machine to a Unix-based Web server without having to worry about the message being changed in any way. The Unix machine is then able to either open the message or direct it to the right place. While most SOAP messages are sent over the Web using HTTP, over e-mail, using SMTP is also an option.