Back in the day, there were different folks trying to solve the same problem: how to make things you find online easily and reliably retrievable despite the people hosting those things regularly giving web pages and other content descriptive names based on where they were within their websites and then wanting to reorganise said websites and change the links to those pages every once in a while.
Two different solutions were proposed and became popular independently: the digital object identifier scheme and permalinks.
The word permalink is a contraction of “permanent link”. Permalinks are web addresses that identify a document or webpage that is expected to work for as long as the thing it links to remains available on the web.
Often eresource records will clearly label the permalink for a journal article. In general, permalinks are short and end with a long number or other code that serves as a unique ID for the webpage or document. For example, the permalink for this blog post is http://www.liblog.port.ac.uk/blog/2020/05/25409/.
Digital object identifiers (DOIs)
The Digital Object Identifier (doi) scheme invited people publishing documents to the web to obtain a doi code (these typically begin 10.1…). These could be copied and pasted into the online doi resolver to find the original article. Later, people started making doi codes into permalinks that could be clicked on to visit the thing they represented. Any doi code can be made into a working permalink by adding https://doi.org/ to the start of the doi code (with no spaces).
These days, doi codes can be turned into just one type of permalink.
DOIs, permalinks and APA (6th ed.) referencing
For some reason (not a logical one, as far as I can tell), APA 6th ed. insists that we should all give the doi link wherever a doi is available in references (in the reference list). Otherwise, we are allowed to use another form of permalink.
Hopefully, this clears up some confusion about these relics from the earlier days of the web. If you have any questions, please chat to us online and we will be happy to answer any questions you may have.