That's from Steve Jin's book about the vSphere API and SDK. http://www.amazon.de/VMware-VI-VSphere-SDK-Infrastructure/dp/0137153635/
Even if it's written for vCenter 4, most of the data model is still the same in version 5.x. The book is highly recommended, even if it focuses on the VI Java SDK, because it contains a lot more of these UML charts (the one above is the one you need most, though :-)
Cheers,
Joerg