When a client calls a Web Service, the transactional behavior of the service is managed entirely on the server side. The method that is exposed as a Web Service can use standard transaction demarcation techniques, but the calling client has no control over this.

There are some practical considerations you should be aware of. If a single Web Service call attempts to perform some operation, and the operation fails, the operation can be rolled back (provided that the Nucleus method is demarcated properly). However, a transaction cannot span multiple Web Service calls so if an operation is performed by a sequence of Web Service calls, and the final call fails, there is no way to roll back the steps performed by the previous calls.