      +--------+       +--------+        +--------+       +---------+      +---------+      +--------+
      |   a    |       |   c    |        |   e    |       |  user   |      |students |      |   g    |
      |        |       |        |        |        |       |         |      |         |      |        |
      +--------+       +--------+        +--------+       +---------+      +---------+      +--------+
         |                |                |                |                |                ^       
         |                |                |                |                |                |       
triangle (default)     diamond          circle         one to many     many to many         mixed     
         |                |                |                |                |                |       
         v                v                v                v                v                v       
      +--------+       +--------+        +--------+       +---------+      +--------+       +--------+
      |   b    |       |   d    |        |   f    |       | orders  |      |courses |       |   h    |
      |        |       |        |        |        |       |         |      |        |       |        |
      +--------+       +--------+        +--------+       +---------+      +--------+       +--------+
