SOAP
SOAP is a protocol specification for XML-based information that distributed applications can use to exchange information and hence interoperate. It is most often accompanied by a set of SOA middleware interoperability standards and compliant implementations, referred to (collectively) as WS. SOAP and WS together define many standards, including the following:
An infrastructure for service composition. SOAP can employ the Business Process Execution Language (BPEL) as a way to let developers express business processes that are implemented as WS * services.
Transactions. There are several web-service standards for ensuring that transactions are properly managed: WS-AT, WS-BA, WS-CAF, and WS-Transaction.
Service discovery. The Universal Description, Discovery and Integration (UDDI) language enables business.
Reliability. SOAP, by itself, does not ensure reliable message delivery. Applications that require such guarantees must use services compliant with SOAP's reliability standard: WS-Reliability.