1. A method for managing data provided from a plurality of systems, comprising: providing a set of objects for data; providing a set of classes for the data; maintaining a catalog with an entry for each data instance of the data; in the catalog, identifying for each data instance its source system and its level of harmonization with other data from the plurality of systems; applying a set of harmonization rules to the data to identify a group of related data and an owner of the group of data; identifying differences in instantiations in the group of data; and initiating an update request to an affected system of the plurality of systems having the differences, wherein the data is accessable by a central data processing system which stores a copy of the data and selectively initiates the update requests.