Publisher Item Identifier
The Publisher Item Identifier (PII) is a unique identifier used by a number of scientific journal publishers to identify documents.Publisher Item Identifier as a means of document identification, Elsevier web site, last update 9 April 1998, accessed October 2003 It uses the pre-existing ISSN or ISBN of the publication in question, and adds a character for source publication type, an item number, and a check digit.