this link might help you - it is the v3 api: https://github.com/openstack/identity-api/blob/master/openstack-identity-api/src/markdown/identity-api-v3.md (https://github.com/openstack/identity...)

in short: Domain - represent a collection of both projects and users Groups - represent a collection of Users and are owned by a specific domain Tenants - is being renamed to Projects Projects -represent the base unit of "ownership" in OpenStack