1. A system for exchanging data between an object-oriented system and a relational system having tables defining a relational model, the system comprising: at least one object class definition defining an object model; an object relational mapping data structure defining a mapping between the object model and the relational model, the object relational mapping data structure produced from a declarative ORM Specification based on an ORM grammar; an exchange unit for translating data from the object model to the relational model and for translating data from the relational model to the object model.