library not found

Hi all,

I'm writing a code in vhdl-ams but I have an error:

use ieee.electrical_systems.all;
        |
ncvhdl_p: *E,SELLIB (../sources/comparateur_ent.vhdl,2|8): unit 
(ELECTRICAL_SYSTEMS) not found in library (IEEE).


Clearly, I guess that the library "electrical_systems" is missing (or I 
write it wrong maybe) so my question is: how to insert a library into 
ieee libraries.

Thanks for your help!