code: public void addDependencyGraph(DAGraph<DataT, NodeT> dependencyGraph) {
          this.rootNode.addDependency(dependencyGraph.rootNode.key());
          Map<String, NodeT> sourceNodeTable = dependencyGraph.nodeTable;
          Map<String, NodeT> targetNodeTable = this.nodeTable;
          this.merge(sourceNodeTable, targetNodeTable);
          dependencyGraph.parentDAGs.add(this);
          if (this.hasParents()) {
              this.bubbleUpNodeTable(this, new LinkedList<String>());
          }
      }
docs: Mark root of this DAG depends on given DAG's root.
  
  @param dependencyGraph the dependency DAG