Making the distinction between URI's, URL's, and URN's

Thanks for the awesome article! Now it's a relief understanding the terms, because I was really struggling with it.

Here's short summary of an article mentioned above:

• URIs are identifiers, and that can mean name, location, or both.
• All URNs and URLs are URIs, but the opposite is not true.
• The part that makes something a URL is the combination of the name and an access method, such as https://, or mailto:
• All these bits are URIs, so saying that is always technically accurate, but if you are discussing something that’s both a full URL and a URI (which all URLs are), it’s best to call it a “URL” because it’s more specific.

URI is best used when you’re referring to a resource just by its name or some other fragment. And when you’re giving both the name of a resource and the method of accessing it (like a full URL), it’s best to call that a URL.

I don't know about that article: it was commenting on a standard, which is clear enough on its own. Directly from the actual standard under URI, URL, and URN:

A URI can be further classified as a locator, a name, or both.

An individual scheme does not have to be classified as being just one of "name" or "locator". Instances of URIs from any given scheme may have the characteristics of names or locators or both, often depending on the persistence and care in the assignment of identifiers by the naming authority, rather than on any quality of the scheme. Future specifications and related documentation should use the general term "URI" rather than the more restrictive terms "URL" and "URN" [RFC3305].

"name" or "locator" is a characteristic of the particular URI, regardless of the scheme. I've seen http: URIs that don't resolve to anything in a web browser, yet are used for naming something that never changes (XML namespaces); they're clearly URNs. If a webmaster is fairly careless, resource URIs may change all the time, so the URI acts more as locator (where the resource happens to be now) than as name (a persistent identifier). If a URL is stable (ie, cool), then it's also a name/URN. It's all up to the authority creating the identifiers.

Moreover, the URI definition is quite clear:

URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]

URIs are always full: scheme and all. Fragments aren't called URIs: they're just incomplete or partial URIs. Calling a fragment a URI is like calling a tire a car: imprecise, not better.

I'd say if you want to stress the URI resolves as the naming components suggest, then call it a URL. If you want to stress that it can serve as a stable name, then call it a URN. However, if you want to always be right, or it doesn't matter, call it URI as the standards do.

The standard is clear by itself without muddled articles.

Thanks a lot for your post! That made clear understanding of the difference.

Very interesting, thank you!

Thank you for sharing that :) It helped a ton. Wish we could upvote your post!

Upvote!