@Override
  public String getVersion() {
    HostComponentStateEntity stateEntity = getStateEntity();
    if (stateEntity != null) {
      return stateEntity.getVersion();
    } else {
      LOG.warn("Trying to fetch a member from an entity object that may "
          + "have been previously deleted, serviceName = " + getServiceName() + ", "
          + "componentName = " + getServiceComponentName() + ", " + "hostName = " + getHostName());
    }

    return null;
  }
The {@link AlertDefinitionCommandTransition} is used to capture the
transition from {@link State#INSTALLING} to {@link State#INSTALLED} so that
the host affected will have new {@link AlertDefinitionCommand}s pushed to
it.
ambari-server/src/main/java/org/apache/ambari/server/state/svccomphost/ServiceComponentHostImpl.java