- \Hypertext and Hypermedia," Academic Press,
Data abstractions, i.e., aggregation and generalization, are useful for representing complex objects eeectively. They provide high level semantic constraints as well as extend the capabilities of entity description in the E-R model. However, corresponding concepts of relationship abstraction are not directly available, particularly in hypertext systems. We propose two types of relationship abstractions, augmentation and globalization, aiming at the improvement of relationship design phases. The former is an abstraction which turns information held in relationships into that of attributes for existing entities. The latter is an abstraction which generates global-to-local relationship hierarchies. We show the advantages of these abstractions.