Object property restriction based on Data property

Question

I'm using Protégé to define an ontology and I'm having trouble defining constraints.

Let's say I have a class "Node" and the Node can be related to other nodes and so on (creating a hierarchical tree). Each node as a data property with a corresponding level.

While I can define domain and range for the property, and define that the class Node has a restriction on this property (only Node values), I don't see any way to define that a Node can only be related to a Node with a lower level.

Any ideas on how to do this using OWL?

Thanks