EMA C++ RDM Usage Guide : 4 Source Directory Domain : 4.4 Special Semantics : 4.4.7 Client Requests Non-Existing Service Directory
 
4.4.7 Client Requests Non-Existing Service Directory
If the client sends a directory request without specifying service name or service ID, the directory response includes all available services. If the client specifies a service name or service ID in a directory request, it receives the directory response for just the requested service. If the requested service name or service ID is not available, Enterprise Message API should send a service directory containing an empty map entry in the payload. If the service becomes available later, the client receives an update message which contains the required service information.
 
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