7) Hotel Management System ER Diagram:

                                    +-------------+
                                    |   Guest     |
                                    +-------------+
                                    | guest_id (PK)|
                                    | name        |
                                    | email       |
                                    | address     |
                                    +-------------+
                                            |
                                            |
                                  +---------+---------+
                                  |                   |
                          +-------+-------+   +-------+-------+
                          |     Books     |   |     Room      |
                          |     Room      |   +---------------+
                          +---------------+   | room_id (PK)  |
                          | booking_id (PK)|   | type          |
                          | guest_id (FK)  |   | capacity      |
                          | room_id (FK)   |   | status        |
                          | check_in_date  |   +---------------+
                          | check_out_date |
                          +---------------+