permanent Internet address

What is a "permanent" Internet address?

If you use electronic documents in your work such as e-books and articles from electronic journals, it is important to include a reference. You should not use the URL, i.e. the address displayed in your browser. This URL can easily change if the publisher is purchased by another company or if your search for the document was bound to a specific session. For this reason, electronic documents have a "durable" address on the Internet. This may be a URN (Uniform Resource Number) or a DOI (Digital Object Identifier).