How to recognize different kinds of documents

The ISSN (International Standard Serial Number) is a unique identifier for a serial. It'a assigned by an international agency and it's the only way to correctly identify journals with very similar or even identical titles.  

It's composed by 8 digits, divided in two 4-digits groups by a hyphen.

Print and electronic version of the same journal have different ISSNs . There's a database, called ISSN portal , where it's possibile to search for the ISSNs of each journal.               

Example.:
the Nursing journal, published by Oxford,  has got ISSN 0142-0372.

The Spanish edition of the same journal has got a different ISSN: 0212-5382