Hello Wartkes,
There could be multiple ways to do this. But it purely depends on the business requirements and user intuitiveness that has to be accommodated.
One simple option I could think of: (disclaimer not sure if it fits with your business requirement)
Designing Domain model is purely based on business needs and UX design. It might be better, if you can explain little bit more about your requirement. And post screens shots of your domain model to get appropriate answers.
- Nirmal