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Data replication is a process to transfer large amounts of data from a source cluster to a target cluster.
As a typical scenario, one could first update any storefront data (like product data) and other settings in an "editing system" and then transfer this information to a "live system". This mechanism allows to develop and maintain large content in the background without significant disturbances to the production system.
The mechanism for transferring individual business objects in an ad-hoc manner is called object replication (developer and administrator perspective) or publishing (shop manager perspective).