SOAP or Simple Object Access Protocol is a protocal which is used for exchanging structured information in the web service implementation in the computer networs. For message formats it relies on XML (Extensible Markup Language) and for message negotiation and transmission it relies on Application Layer Protocols (like HTTP) and Simple Mial Transfer Protocol (SMTP).
Features of SOAP:

1. It is a communication protocol
2. It is used for communication between applications
3. It is a format which is used for sending messages
4. It communicates via Internet
5. It is platform independent
6. It is language independent
7. It is based on XML
8. It is simple and extensible
9. It allows to get around firewalls
10. It is a W3C recommendation

Builiding Blocks of SOAP:
SOAP message is a a simple XML document which includes below elements:

1. An Envelope element that identifies the XML document as a SOAP message
2. A Header element that contains header information
3. A Body element that contains call and response information
4. A Fault element containing errors and status information

SOAP Syntax Rule: Below are some important syntax rule:

1. A SOAP message MUST be encoded using XML
2. A SOAP message MUST use the SOAP Envelope namespace
3. A SOAP message MUST use the SOAP Encoding namespace
4. A SOAP message must NOT contain a DTD reference
5. A SOAP message must NOT contain XML Processing Instructions

SOAP Document example ... ... ...