Relations between SAP AII, ONS, PML and Savant???

The EPCGlobal provides a standard EPC-Network containing the EPC-Code and infrastruture-components like the RFID-Tag and -Reader, the ONS-Server, the PML-Server and a RFID-Middleware called Savant.

On the one hand I found a couple of articles where the SAP Auto-Id Infrastructure (SAP AII) is said to be a "RFID-Middleware". On the other hand I found a lot of presentation sheets with illustrations of the SAP AII architecture where the SAP AII is connected to Savant by the device controller and to the ONS/PML Servers by SAP XI.

Can anybody inform me about the relationship between the SAP AII, the ONS/PML Servers and Savant? Is the SAP AII a substitute for Savant? Which component of the SAP Auto-ID Infrastructure asks the ONS-Server for the URL to a PML Server where further information about an object which is identified by the EPC code are located? Are product information stored on a PML-Server anyway? Or are information only stored in the ERP-Backendsystem?

Thank you for your reply.