Library books are arranged by the Dewey Decimal classification scheme whereby each subject is represented by a number.
You wil find books on the same subject will have the same number. The shelfmark is preceded by the letter D and will be followed by 3 letters, which are usually the first 3 letters of the author's name.
Here are some useful CIS shelfmarks.
D 003 Systems
D 020 Library and information sciences
D 029 Information science
D 005 Computer programming