A set in structure (SIS) list is established for each DAG structure of a DAG structure network. Additionally, a used before set (UBS) list is established for each structure invoking element in the DAG data structure. At each invocation of a DAG structure, a list of traversal state list (TSL) attribute...http://www.google.com/patents/US5430870?utm_source=gb-gplus-sharePatent US5430870 - Saving and restoring traversal state attributes of a directed acyclic graph structure network for a parent structure when it invokes a child structure for traversal
