There are three types of hierarchy alerts that occur at the following times:
1. When a node is added or removed from the hierarchy structure – An alert event is sent both up and down the structure
2. When a replication operation completes, an alert event is sent to all nodes of hierarchy structure, which contains information on the amount of data transferred between each node.
3. When a resource is merged, a hierarchy global synchronisation event is sent out to all nodes in the direction the resource came from.