Describes task dependencies
| Column | Type | References | Comments |
| id | Integer | Primary key | |
| vdb_id | Integer | ||
| predecessor_id | Integer | db_task.id | The predecessor task |
| task_id | Integer | db_task.id | The successor task |
| lag_value | Float | Lag duration value | |
| lag_type | Integer | Lag duration type (see task duration for valid values) |