A Survey of Key-to-Key User Hierarchic Representation Mechanisms

This paper discusses some methods of key-to-key user hierarchic representation. For each mechanism, we describe (1) a model for determining the relationship between two users, (2) the memory storage required for keys, and (3) the construction of keys. The common drawbacks of the key-to-key user hierarchic representation strategy are also described. Despite great progress, three important problems remain open.