a file or filegroup cannot useed by one datebase.
a file can be only a member one filefroup.
Data and log cannot be part od the same file.
log file cannot part od any filegroup.
....
a file can be only a member one filefroup.
Data and log cannot be part od the same file.
log file cannot part od any filegroup.
....
A file is a physical allocation of space and can be one of three types:primary,secondary,log.