Your shifts are at multiple companies, each of
which may have one or more addresses, and each address may have one or more
locations within that address.
An example would be a hospital with several
campuses each at their own address, and multiple departments within each
address where shifts are to be carried out.
Another example would be a security company
providing a service for many companies (funding bodies), each of which
requires a service at one or more addresses in their chain, and possibly
several locations (perhaps entrances) within each address.