14. The one or more non-transitory computer-readable storage media recited in claim 11 , wherein the second client web service message contains a request that the server maintain a state of the execution of the XQuery expression, the method further comprising: in response to detecting the request that the server maintain the state of the execution of the XQuery expression, maintaining the state associated with the execution of the XQuery expression.
14. The one or more non-transitory computer-readable storage media recited in claim 11 , wherein the second client web service message contains a request that the server maintain a state of the execution of the XQuery expression, the method further comprising: in response to detecting the request that the server maintain the state of the execution of the XQuery expression, maintaining the state associated with the execution of the XQuery expression. 15. The one or more non-transitory computer-readable storage media recited in claim 14 , wherein the step of maintaining the state of the execution of the XQuery expression comprises responding to the request with a transaction identifier that identifies a transaction of which the operation is a part, the method further comprising: receiving, at the server, a client web service message that contains the transaction identifier; and based on the transaction identifier, identifying, at the server, the transaction of which the execution of the XQuery expression is a part.