If we want to support two-phase commit, we need a protocol that allows flexible designation of the coordinator role. For example, a given web service may be willing to play the role of participant in certain situations, but may insist on playing the role of coordinator in other situations. A service can export a coordinator version and a participant version of the same logical conversation. We believe compensation is a fundamental notion of atomicity for web service, and in the remainder of this paper, we shall only consider compensation. This does not reflect a position against two-phase commit, but is merely to simplify the discussion.
Isolation is unnecessarily strict for Internet transactions.
This is evident from many Internet sites that provide transactions without isolation. Besides being unnecessarily strict in many cases, isolation is also costly because transactions may be long running, and providing isolation for long-running transactions hampers the overall performance. Durability means that transactional updates are made persistent if the transaction completes successfully. Consistency means that a transaction takes the system from one consistent state to another. The durability and consistency of constituent transactions follows from the transactional properties of the backend logic in web services.