A formal model of views for object-oriented database systems

The de nition of a view mechanism is an important issue for object-oriented database systems, in order to provide a number of features that are crucial for the development of advanced applications. Due to the complexity of the data model, the object-oriented paradigm introduces new problems in the de nition of a view mechanism. Several approaches have been de ned, each de ning a particular view mechanism tailored to a set of functionalities that the view mechanism should support. In particular, views can be used as shorthand in queries, can support the de nition of external schemas, can be used for content-dependent authorization, and, nally, can support some form of schema evolution. In this paper, we formally introduce a view model for object-oriented databases. Our view model is comparable to existing view models for what concerns the supported features; however, our model is the only one for which a formal de nition is given. This formal de nition of object-oriented view mechanisms is useful both for understanding what views are and as a basis for further investigations on view properties. The paper introduces the model, discussing all the supported features both from a theoretical and practical point of view. A comparison of our model with other models is also presented.