If a collection is not classified and arranged systematically,
a call number will, obviously, not contain a class mark. Similarly
if books are occasionally displayed in open access and sometimes
taken to closed stacks they may contain two call numbers: one for
open access and one for closed stacks. This is the practice in some
large national and university libraries across Europe. Because of
having to manage meaningless and mechanical codes, as well as
systematic arrangement codes, libraries in continental Europe do
not usually separate the notion of book number, i.e. the symbol for
the book within a larger class, and author mark (symbol assigned
to the author) from the one of call number, i.e. the summary
notation on the book label.