EMA C++ RDM Usage Guide : 4 Source Directory Domain : 4.1 Description
 
4.1 Description
The Source Directory domain model conveys:
Information about all available services and their capabilities. This includes information about domain types supported within a service, the service’s state, the quality of service, and any item group information associated with the service. Each service is associated with a unique ServiceName or ServiceId.
Status information associated with item groups. This allows a single message to change the state of all associated items, avoiding the need to send a status message for each individual item. The consumer is responsible for applying any changes to its open items. For details, refer to Section 4.3.1.2 and Section 4.3.1.3.
Source Mirroring information between an LSEG Real-Time Advanced Distribution Hub and Open Message Model interactive provider applications exchanged via a specifically-formatted generic message as described in Section 4.2.5.