code: public void depends(int parent, int child)
      {
          dag.addNode(child);
          dag.addNode(parent);
          dag.addEdge(parent, child);
      }
docs: Adds a dependency relation ship between two variables that will be in the network. The integer value corresponds
  the the index of the i'th  categorical variable, where the class target's value is the number of categorical variables.
  
  @param parent the parent variable, which will be explained in part by the child
  @param child the child variable, which contributes to the conditional probability of the parent.