A composite object represented as a directed graph is an important data structure which requires efficient support in CAD/CAM, CASE, office systems, software management, Web databases and document databases. It is cumbersome to handle such an object in relational database systems when it involves recursive relationships. In this chapter, we present a new encoding method to support the efficient computation of recursion. In addition, we devise a linear time algorithm to identify a sequence of reachable trees (w.r.t.) a directed acyclic graph (DAG), which covers all the edges of the graph. Together with the new encoding method, this algorithm enables us to compute recursion w.r.t. a DAG in time O(e), where e represents the number of edges of the DAG. More importantly, this method is especially suitable for a relational environment.