Indexed on: 01 Jul '96Published on: 01 Jul '96Published in: Journal of Computer Science and Technology
In complex object oriented databases, the purpose of introducing class hierarchy is to express ISA semantics, to realize inheriting and to reuse schema definition codes. The schema definition and schema evolution, based on the partial order of lattice, often cause the loss of information inheriting and the redundance of schema definition. Based on the fullness of the inheritance shown by class hierarchy, three normal forms of class hierarchy are given in this paper, and a general algorithm of normalization of class hierarchy is presented, following the Boolean algebra model of class hierarchy. The loss of information inheritance can be avoided when they are applied to schema design and schema evolution.