ONTOLOGICAL FOUNDATIONS FOR STATE AND IDENTITY WITHIN THE OBJECT-ORIENTED PARADIGM

Objects can be seen, at an abstract level, as information tokens made of two parts: an identification part and state, or value part. The ide ntification part contains an object identifier different from that of any other object. The state part contains instead a structured value d enoting the collective value of the attributes of the object. While th e identifier assigned to an object remains fixed, the state is allowed to change, i.e. different values can be found in the state part of th e object at different times. An object model with identifiers abstract s the formal properties of identity achieving a neat separation betwee n object identification and object representation. Object identificati on becomes therefore a formal property preserved by the system. Tradit ional approaches in data and knowledge representation use instead some aspects of individuals' state, which only occasionally satisfy the un iqueness and continuity properties of identity. The problem is that id entificative attributes chosen at a given time, may carry different va lues or may not be unique as the context changes; in general, identifi cation is conceptually different from representation. The paper propos es an ontological foundation for the concept of object state and ident ity, showing formally the equivalence with the infinite properties whi ch are inherent in the cognition of real world distinct entities (Leib niz' principle). (C) 1995 Academic Press Limited