A comparison of ORN to other declarative schemes for specifying relationship semantics

Object Relationship Notation (ORN) allows relationship semantics to be specified to an object database management system (ODBMS) when relationships are represented as object-valued class attributes, both singly and multiply valued. Other declarative schemes have been proposed or developed to define semantics for such relationships when they are represented as foreign keys in a relational database or as relations in an extended object data model. In this paper we give an overview of ORN and compare it to these other schemes as well as to the declarative capabilities that currently exist for defining relationships in commercial ODBMSs. The purpose of our comparison is to permit the relative merits of ORN to be appreciated and to underscore the need for such a notation in ODBMSs.