Schema Evolution publication categorizer

We describe the underlying operators and rules of an interactive procedure for merging generalization hierarchies. This procedure assists a designer in defining a global view which is a view over multiple databases. The small collection of operators permit:

(1) connecting generalization hierarchies to form a new hierarchy,
(2) adding and deleting subhierarchies
(3) deleting intermediate levels.

The merging procedure applies the rules in two phases. In the connecting phase, the input generalization hierarchies are connected to form a new hierarchy. The input hierarchies are typically connected at their roots but may be connected at nonroot nodes. In the subtree merging phase, the new generalization hierarchy is revised according to equivalence assertions about the attributes of the subtypes. The rules are described in detail for the case of binary merging. Extensions for the general m-way case are briefly outlined. This set of rules can form the basis of a rule-based expert system.