Rather than grouping them by subject like the Library of Congress or Dewey Decimal systems, SuDocs puts together publications by the agency or department that has published them. The number before the period indicates the issuing bureau of that agency, and the number following the period indicates the type of document. The book number might be based on the main word of the title, the series number or issue number of the document. Since it is an information circular about the Indiana Dunes, Indiana is the main word in the title. The numbers following the letters help distinguish this document from other circulars about the Indiana Dunes.
Some documents are journals, works in a series or annual publications.
These have book numbers that have no letters in them. Years are represented by the last three digits in the year. It is important to remember that all numbers are whole numbers in a SuDocs call number. Examples of this would be the Consumer Product Safety Commission and the Nuclear Regulatory Commission. Congressional Publications Class numbers for Congressional committee hearings and prints all begin with Y 4 .