Identifies the
DomainRing
in an onion architecture. The domain ring is the inner-most ring in the
onion architecture and is only coupled to itself. It models the truth of the business domain by consisting of
behaviour (logic) and the required state (data).
Compared to the 4-ring onion architecture in which the domain is split into domain model and domain services, the
3-ring version combines those 2 rings so that it implements behavior (logic), state (data), and interfaces needed for
e.g. storing and retrieving data, i.e. repository interfaces.