preselection software

[Green, Lori]

Hello-- 
I joined this list during the filtering discussion, so my apologies if
this already has been covered.  I am wondering about preselection
software.  I would greatly appreciate an explanation of its merits (and
as opposed to filters).  Does anyone know of companies and/or vendors
who produce/provide this?

TIA,
--Lori Green
Reference Librarian
Mount Carmel Health System
Columbus, Ohio
lgreen at mchs.com