getArrowMarker(i) {
    let a;
    switch (i) {
      case 0:
        a = "aggregation";
        break;
      case 1:
        a = "extension";
        break;
      case 2:
        a = "composition";
        break;
      case 3:
        a = "dependency";
        break;
      case 4:
        a = "lollipop";
        break;
      default:
        a = "none";
    }
    return a;
  }
Gets the arrow marker for a type index

@param type - The type to look for
@returns The arrow marker