URIs URNs and URLs: What's the difference

What's a URI and how is one different from a URL?

URI stands for "Uniform Resource Identifier", meaning a string (sequence) of characters that can uniquely identify anything on the internet. URL stands for 'Uniform Resource Locator', meaning a string of characters that indicate where something can be found. By analogy, think of a Social Security (SSN) number that uniquely identifies a person; that person will also have a street address where they can be reached by mail or visited in person. The SSN is similar to a URI in that it won't change, but the address might. In Linked Open Data, it is one best-practice to use a URL as the URI for any publicly available web-based resource that can be easily re-used by others. Meaning, the string 'http://opencontext.org/subjects/6A48C92B-E9DB-4CA0-1F9E-2F3ECEFC1C7C' is both the permanent identifier for that page describing a coin found at Petra, and the location where that page can be found. OpenContext goes a long way to making this clear by offering a 'Suggested Citation' that includes the URI. In general, combining the roles of URI and URL, which requires a commitment to the permanence of URLs, enables many of the benefits of Linked Open Data. In this context, 'URI' is often the preferred term within Digital Humanities and Linked Open Data. This usually means that in casual conversation, you can replace with 'URL' with 'URI' whenever somebody is talking about permanent, high-quality web-based resources.

See also Very clean URIs.

What's a URN?

Answer pending