An internationally recognized voluntary numbering system for the identification of audiovisual works. The ISAN is similar to the ISBN (International Standard Book Number) system for the identification of books. The ISAN is a 16-digit number consisting of a 12-digit root segment and a 4-digit segment for the identification of episodes or parts when applicable. A check digit is added whenever the ISAN is presented in human-readable form. The ISAN identifies the work rather than the content of the work or actual publications. There is no relation between the ISAN and copyright registration. The standard was developed by the International Standards Organization (ISO).