Sequence diagrams for synchronous and asynchronous XMPP cloud services. XMPP services may be implemented in the traditional synchronous way that directly returns the result when a method is invoked (A). Alternatively, services that perform time-consuming operations may be implemented in an asynchronous way where the client is notified after the initial job submission about the completion of the remote process, and the client subsequently requests the result from the service (B). The crosses indicate the end of a thread.
Wagener et al. BMC Bioinformatics 2009 10:279 doi:10.1186/1471-2105-10-279