In [Touretzky et al., 1987] and [Selman and Levesque, 1989], a brief comparison between upward and downward view of inheritance reasoning is given. In this paper, we review the evolution of inheritance networks, and analyze systematically, the downward (property flow) and upward (individual flow) views of inheritance for different categories of networks. We observe that both these views assign the same meaning to tree-structured hierarchies, and explain the divergence in the interpretation of more general inheritance networks in terms of their expressive power. This simple analysis sheds light on the inherent nature of nonmonotonic inheritance. In addition, we also describe the notion of preferential inheritance to specify additional conflict resolution information, which can be integrated smoothly with the upward view of inheritance.
Available at: http://works.bepress.com/tk_prasad/49/