A Relational Object Model

The relational model and its extensions are often considered incompatible with object-orientation. However, on the one hand nested relations provide the complex object features demanded by object models. Particularly, powerful query languages exploit the complex data structure while keeping the advantages of the declarative, set-oriented paradigm. On the other hand, object models provide semantically rich constructs for advanced modeling, and abstractions of operations as well as data. In this paper, we show an evolutionary path from relational, essentially nested relational, to object-oriented data models and query languages. Basically, allowing nested relation schemes to be recursively defined yields the necessary flexibility w.r.t, structure. The query language, i.e., nested relational algebra, carries over to this "network" model. As a first step towards the object-oriented integration of cooperative systems, different views onto the objects have to be supported. We present a powerful view definition facility that basically allows object views as well as relational views to be defined in our object algebra.