Viewpoints Handling in an Object

Traditional class-based object-oriented data models and programming languages do not allow an object to have several types or to play diierent roles while keeping the same identity. Therefore, the modeling of persistent evolving entities is a diicult task. Some speciic models and languages exist, but do not support some of the features of traditional OODB models such as inheritance, late binding or common implementation through the notion of class. In this paper, we propose an object model that extends the one proposed by the ODMG while keeping the statical strong type-checking property of the programming language. The model is based on the novel concept of criterium-based class, from which instance objects have an immutable identity and several viewpoints which are accessible through a single interface. The model allows to consider new features such as property sharing and viewpoints merging, unconsidered so far, in a clean and homogeneous way.