1. A network of peer-to-peer enterprise information systems comprising: a first source system for publishing a data change of an attribute of a first entity of the first source system, wherein said first entity is one of a first plurality of entities; a unified entity-relationship system comprising said first plurality of entities, said first plurality of entities each comprising a plurality of attributes; at least one subsumed entity-relationship system coupled to said unified entity-relationship system, wherein said first plurality of entities of said unified entity-relationship system are mapped to one another and to a second plurality of entities and attributes of said second plurality of entities of said subsumed entity-relationship system; a join engine peer coupled to said unified entity-relationship system for performing joins and splits to form related entities according to a join model; a global object model coupled to said join engine peer, said global object model comprising a first mapped relationship of said mapped relationships and said join model specifying transformations and queries required for forming a second entity from a set of related entities, wherein at least one of said set of related entities is obtained from a second source system, and wherein said first mapped relationship is used by said join engine peer to enforce data consistency between said first entity and said second entity; and a third source system for storing said data change in said second entity formed by said join engine peer.