What is a Persistent Link?
Persistent links are links to specific web pages or web resources that remain stable over time. Persistent links go by a number of names, including permalink, permanent link, permanent URL, persistent URL, PURL, durable link, or durable URL.
Many are unaware that links, especially with subscription and licensed content systems and similar account-based systems, are often session-based and only work for the duration of your search session. If you try to access a session-based link after you navigate away from the page or a few hours later, you will get an error message instead of the page or resource you were expecting.
Why should I use a Persistent Link?
Linking to a resource means that you are not making a copy of it. You are simply pointing to an item and are much more unlikely to be infringing on copyright or violating licence agreements. Therefore, persistent links are a preferred method for you to share resources with others.
The link displayed in a web browser’s address bar after a search is done is not necessarily persistent (i.e. bookmarkable), because it may incorporate passwords or session variables, which expire once the browser is closed.
Testing Your Link's Persistence
A good way to test the URL is to bookmark the page, close all browser windows, re-open the browser, and check the bookmark to ensure that you can still get to the resource.
Illustrations of persistent linking can be found here.