Library catalogers use classification systems to determine the call number you see on the spine of a book or piece of library material. The systems are intended to categorize knowledge logically. From a practical perspective it allows library personnel to shelve the books in a specific order, and, more importantly, allows people to find the material on the shelves. Two systems are widely used; the Library of Congress Classification System (LC) and the Dewey Decimal Classification System (DDC). This library uses both. The main collection is cataloged using LC and the juvenile collection uses DDC. Government documents are cataloged using another system entirely, the SuDoc system, which will be discussed later.