1. An apparatus comprising: a shared database organized around a common schema defined by metadata, the shared database being shared by multiple users having access to different subsets of the data in the shared database; a first application to provide access to the shared database using the common schema, the first application having a purchased first schema extension received from a first identified user, the first schema extension being defined by metadata and having a first set of additional objects, the first set of additional objects being defined by the first application, the first schema extension making changes to the common schema metadata to change a view of an object of the shared database and wherein the first application tracks the changes to the common schema metadata; and a second application to provide access to the shared database using the common schema, the second application having a second purchased schema extension received from a second identified user, the second schema extension having a second set of additional objects, the second set of additional objects being defined by the second application, wherein the first and second applications present views of and operations on the shared database that are extended by the respective schema extension.