All cells in the i2b2 hive communicate using standard, pre-defined i2b2 XML request and response messages.
A request message is sent from a client to a service and contains information inside the top level <request> tag that allows the service to satisfy the request. The <request> tag contains a <message_header>, <request_header> and <message_body>.
The service sends back a response message, inside a top-level <response> tag, which informs the client about the status of the request and may also contain the actual results. The <response> tag contains its own <message_header>, <response_header> and <message_body> and it may optionally echo the request's <request_header>.
The following image illustrates the basic top-level elements contained within the request and response messages.