Reference document

Transaction Services
The Transaction Services allow multiple individual operations to be linked together as a single, indivisible action. All operations in a transaction are either completed without error or none of them are; if some of the operations are completed but errors occur when the others are attempted, the transaction-processing system “rolls back” all of the operations of the transaction (including the successful ones) thereby erasing all traces of the transaction and restoring the system to the consistent, known state that it was in before processing of the transaction began. In scenarios when usual transactional properties (like atomicity, consistency, isolation, and durability) are too strong or unimplementable (e.g. in complex business processes), some limited transactional properties must be satisfied to guarantee a process is not left in an inconsistent state. For example compensating activities can bring the process to a consistent state, albeit not necessarily identical as the state before the process started.
Composition Services