1. A system comprising: a) a master reference manager for maintaining master reference data sets of an enterprise, each master reference data set uniquely identifying a particular entity and representing a best version of reference data maintained for the particular entity; b) a hierarchy manager for managing relationship data sets for the entities identified by the master reference data sets, each relationship data set expressing a relationship that the particular entity has with at least one other entity, said hierarchy manager managing the relationship data sets by aggregating the relationship data sets for the entities identified by the master reference data sets, wherein said hierarchy manager aggregates the relationship data sets by: i. receiving relationship data sets that are stored in a plurality of data storages, each data storage storing relationship data sets in a particular application-centric format, ii. converting said relationship data sets from the particular format into an enterprise-normalized format, said enterprise-normalized format defied for specifying relationship data for the enterprise, and iii. storing the enterprise-normalized relationship data set in a master data store.