title_body: Do epub and paperback publication of same book need seperate Identification number (like ISBN)?
upvoted_answer: First, we need to distinguish what is what code is used for. Some code do not describe books (ISSN, ISMN, URN). Others describe library sorting (LCSH, DDC), where these systems were built long before computers and electronic books (LCSH - 1898, DDC - 1876). And there is not a complete practice of dealing with this.
  
  
  ISBN - International Standard Book Number
  
  This is for books. Practice is such that every format (Epub, PDF, Mobi, DjVu etc.) has own ISBN. (It should be.) Sometimes a paperback and a hardcover book have their own ISBN code.
  
  
  ISSN - International Standard Serial Number
  
  This is for periodicals (magazines, a periodically published series of books etc.) It is not required in my country. Perhaps it will be similar in other countries. What I know, the code should be the same (for paper and digital copy).
  
  
  ISMN - International Standard Music Number for Printed Music
  
  This is for music. No for ebooks.
  
  
  URN - Uniform Resource Name
  
  URN uses a "urn" scheme and does not address the availability of the identified resource. This is prefix example for ISBN and ISSN.
  
  urn:isbn:0451450523
  urn:ISSN:0167-6423
  
  
  
  LCSH - Library of Congress Subject Headings
  
  I am not American. I do not know how you handle it. I recommend visiting the congress library web site.
  
  
  DDC - Dewey Decimal Classification or Dewey Decimal System
  
  I suppose it should be taken as another edition of the book. What I know is distinguished by the letter (one character) at the end (in my country). But library practice may vary.
  
  
  Summary:
  
  ISBN - different
  ISSN - same + postfix
  DDC  - same + postfix