Overview#DirXML command are the output of a driver channel.
When the DirXML Shim sends an event notification to DirXML Engine, the DirXML Shim is informing DirXML Engine of a change in data that occurred in the Connected Application. DirXML Engine then determines, based on configurable policies, which DirXML commands, must be sent to the Identity Vault namespace.
When Identity Manager sends a command to the shim, Identity Manager has already taken an Identity Vault event as input, applied the appropriate policies, and determined that the change in the connected system represented by the command is necessary.
From the point of view of the overall system, if a command from one driver on its Publisher channel is creating or updating an object in the Identity Vault, it might cause events to be submitted on the Subscriber channels of other drivers in the system. This allows changes to cascade, flowing to all connected systems.