Publisher Item Identifier

The Publisher Item Identifier (PII) is a unique identifier used by a number of scientific journal publishers to identify documents. 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.

The system was adopted in 1996 by the American Chemical Society, the American Institute of Physics, the American Physical Society, Elsevier Science, and the IEEE.

Format
A PII (pii) is a 17-character string, consisting of: When a PII is printed (as opposed to stored in a database), the 17-character string may be extended with punctuation characters to make it more readable to humans, as in Sxxxx-xxxx(yy)iiiii-d or Bx-xxx-xxxxx-x/iiiii-d.
 * one character to indicate source publication type: "S" = serial with ISSN, "B" = book with ISBN
 * ISSN (8 digits) or ISBN (10 characters) of the serial or book to which the publication item is primarily assigned
 * in the case of serials an additional two digit number to pad the difference between the 8-digit ISSN and an ISBN (suggested are the last two digits of calendar year of the date of assignment, which is not necessarily identical to the cover date)
 * a 5-digit number assigned by the publisher that is unique to the publication item within the serial or book
 * a check digit (0-9 or X)