Peter, in the Installation and Setup Guide that Malar references, there are also sections that describe the Core and Host Packages: "Contents of the OnCommand Core Package" and "Contents of the OnCommand Host Package". This information might help clarify some of your questions. There is also an architecture graphic in the "OnCommand architecture" section.
Please let me know if there are questions remaining that are not answered by the introductory information in the guide so that we know what to consider adding for the next release.
Thanks!
Beverley
MEI Technical Writer