a set consists of circular linked lists where one record type, the set owner or parent, appears once in each circle, and a second record type, the subordinate or child, may appear multiple times in each circle. in this way a hierarchy may be established between any two record types, e.g., type a is the owner of b. at the same time another set may be defined where b is the owner of a. thus all the sets comprise a general directed graph (ownership defines a direction), or "network" construct. access to records is either sequential (usually in each record type) or by navigation in the circular linked lists.