You want to know the purpose of the Dwhwizrd.exe file.
The Dwhwizrd.exe file is used when a new set of definitions comes in. If you set debug mode to "verbose" and copy a new .vdb file into the directory where NAV is installed, then Dwhwizrd.exe pops up a window that reports what it is doing. The window flashes by quickly, but the corresponding line in the Rtvscan.exe debug window is "Pattern File <path>