Schema Transformation processors for federated objectbases

In contrast to three Schema levels in centralized object-bases, a reference architecture for federated objectbase Systems proposes five levels of Schemata. This paper investi-gates the fundamental mechanisms to be provided by an object model to realize the processors transforming be-tween these levels, namely Schema extension, Schema fil-iering, and Schema composition. It is shown, how compositum and extension are used for stepwise bottom-up integration of existing objectbases into a federation; and how extension and filtering support authorization on dif-ferent levels in a federation. A powerful View definition mechanism and the possibility to define subschemata (i.e., parts of a Schema) are the key mechanisms used in these processes.