| 1 | Parent |
| A code to indicate a parent relationship. |
| 2 | Child |
| A code to indicate a child relationship. |
| 3 | Peer, internal |
| A code to indicate an internal peer relationship. |
| 4 | Peer, external |
| A code to indicate an external peer relationship. |
| 5 | Finish to start constraint |
| A code to indicate a finish to start constraint relationship. |
| 6 | Start to start constraint |
| A code to indicate a start to start constraint relationship. |
| 7 | Finish to finish constraint |
| A code to indicate a finish to finish constraint relationship. |
| 8 | Start to finish constraint |
| A code to indicate a start to finish constraint relationship. |