1. A system comprising: a data integration subsystem configured to maintain a baseline data structure representing a base set of data relationships, said data integration subsystem being further configured to maintain a mapping of said baseline data structure to local data maintained by a plurality of local data subsystems; and a portal subsystem configured to provide a first customizable data structure associated with said baseline data structure for access by an external party, create a copy of at least a subset of said baseline data structure, and provide a second customizable data structure associated with said copy of said baseline data structure for access by said external party; wherein said first customizable data structure and said second customizable data structure are independently customizable to represent different custom sets of data relationships.