Her er et ER-diagram for et jernbanestyringssystem:
```
+----------------+ +--------------+
| Tog | | Ruteplan |
+----------------+ +--------------+
| id (PK) | | rute_id (PK) |
| nummer | | src_station |
| ankomsttidspunkt | | des_station |
| afgangstid | | afstand |
| pris | +--------------------+
+----------------+
| |
| |
V V
----------------------------
|
Station
+----------------+
| station_id (PK) |
| stationsnavn |
| by |
+----------------+
--------------------------
|
+----+----------+
| | |
V V V
Medarbejderpassagerbillet
+------------+ +-------------+ +---------+
| emp_id (PK)| | id (PK) | | billet_id|
+------------+ +-------------+ +---------+
| emp_name | | navn | | dato |
| emp_type | | alder | | tognummer |
| løn | +-------------+ | |
| | | |
| | ------
V ----------
----------------------
Reservation
```
