Inventory Hierarchies and
ServiceInstance
When you start a session, vSphere creates a
ServiceInstance
with one root
folder, one
Datacenter
, and four folders that
hold the different types of inventory objects.
When you access a vCenter Server System, the
hierarchy shown in the illustration below allows you to traverse the inventory.
vCenter Server Inventory Hierarchy

If your
ESXi hosts are managed by vCenter Server, you must always access your hosts
through vCenter Server. The vCenter service keeps track of all synchronous and
asynchronous operations, and will have the latest status and inventory
information about each ESXi host. Therefore, connecting directly to a managed
host may give you incorrect or incomplete data.
When you have ESXi hosts that are not managed by
vCenter Server, your application can connect to each host directly.