A method for using a data model to enable authorization and communication between computers including a first computer configured to provide a service, a second computer in communication with the first computer, and a third computer in communication with one or both of the first computer and the second computer. The method includes storing the data model, wherein the data model describes nested party relationships among a first party having access to the first computer, a second party having access to the second computer, and a third party having access to the third computer, wherein the data model describes the third party as a third set of attributes specifying authorizations of the third party with respect to only the second party, the third set of attributes being nested within and dependent upon a second set of attributes specifying authorizations of the second party with respect to the first party.