Library Simprim cannot be found?

hello! When I use ths XST to synthesis(Simulate Post-translate VHDL Modele) a project,it tells me errors: ERROR:HDLParsers:3317...Library SIMPRIM cannot be found. ERROR:HDLParsers:3013...Library SIMPRIM is not declared.

library SIMPRIM; use SIMPRIM.VCOMPONENTS.ALL; use SIMPRIM.VPACKAGE.ALL;

why?How to do it?

Thanks!