Comment by bertails

> How does this relate to domain-driven design?

The "Domain" in `upper:DomainModel` is the same D as in DDD (Domain-Driven Design) as the D in DGS (Domain Graph Service).

> in DDD it's kind of expected that the same concept will be represented in a different way by each system

In UDA, those concepts would explicitly co-exist in different domains. "Being the same" becomes a subjective thing.