Alumni Library organizes its collections by subject. These subjects are represented by a call number system called the Dewey Decimal Classification System (DDC). DDC uses call numbers that begin with numbers.

If you were looking for the book 'Yin Yu Tang : The Architecture and Daily Life of a Chinese House' by Nancy Berliner using the online catalog you would find that the call number is 720.951 .B47 2003.

720	The main number can be any three-digit number between 001 and 999. This identifies the broad subject category the item is classified in. In this case 720 denotes 'architecture.'
.951	Any number following the decimal further specifies within the broader category a narrower subject. In this case the .951 stands for China. In this way all architecture items about China will gather next to each other on the shelf. This number is a true decimal number, this means that 720.951 will be shelved before 720.96 on the shelf because it's a smaller number.
.B47	The third section describes the author. The .B47 stands for the author's last name (Berliner)
2003	The book was published in 2003