title: Airflow - is depends_on_past and trigger_rule the same?
body: <p>In airflow.models.BaseOperator. You have two default parameter:</p>
  <p><code>depends_on_past=False</code> and <code>trigger_rule=u'all_success'</code></p>
  <p>According to doc</p>
  <blockquote>
  <p>depends_on_past (bool) – when set to true, task instances will run sequentially while relying on the previous task’s schedule to succeed.</p>
  <p>trigger_rule (str) – defines the rule by which dependencies are applied for the task to get triggered.</p>
  </blockquote>
  <p>Isn't both the same thing ? I don't get why there are redundant parameters.</p>