5. A computer-implemented metadata repository comprising: at least one storage device storing: first metadata defining a first object model including extensible entities, the first object model comprising an instance of a metaobject; second metadata defining an extension object model, the extension object model to extend at least one of the extensible entities of the first object model; and executable program code of a service to merge the first object model and the extension object model to create metadata defining an extended object model, the extended object model comprising an instance of the metaobject, the merge including identification of a node of the extension object model pointing to a node of the first object, addition of the node to the first object model when the node of the extension object model is not an addressing node, and not add the node to the first object model when the node of the extension object model is an addressing node; the executable program code of the service further to receive a request for data associated with an instance of the first object model, and to retrieve data associated with the instance of the first object model based on the metadata defining the extension object model, wherein the extension object model comprises an instance of the metaobject; and a processor to execute the executable program code.
6. The computer-implemented metadata repository according to claim 5 , wherein a namespace of the added node is different from a namespace of the node of the first object model.