>mortality</code>.</p>
<p>A good metaphor for a DAG is a network of <em>one-way</em> streets. On a one-way street, you can drive your car in one direction but not the other. In a DAG, <em>influence</em> flows in only one direction for any given link.</p>
<p>The one-way street network metaphor fails in an important way. Influence is not the only thing we need to keep track of in a DAG. <em>Information</em> is another entity that can seem to “flow” through a DAG. To illustrate, consider this simple DAG:</