.db file is only the compiled of .lib (liberty) file. the compilation is made by lc_shell, library compiler, a tool from synopsys as well.
we could beleived, the .db is "more" rapidly ready by the synopsys tool, than the liberty file.
.db & .lib should contains the same timing/power/area../ informations, because the library compiler only read the liberty and write .db without other inputs.
Both .lib and .db are synopsys logical library modeling formats.library compiler converts .lib to .db format.these .db files are in binary format whereas .lib in ASCII format. Before a library can be used, it must be compiled to .db.