URL? URI? URN?!?
Posted by Jon Lee in Offtopic, Web Development, tags: terminology, URI, URL, URN, web development
If you’ve ever posted a comment on a Wordpress blog, you may notice that it asks for your name, e-mail and URI. Ever wonder why it says URI and not URL? Do you know what the difference is and which one is correct? This post is more of a terminology lesson than anything but I think it’s important to use the correct terms!
URI stands for Uniform Resource Identifier. It is a string that is used to identify or name a resource. URI’s are most often associated with the Internet although they can be used elsewhere as well. The following are examples of URIs:
- http://www.jonlee.ca
- ftp://randomhost.com/directory/file.txt
- /usr/bin/data.txt
- ISBN: 978-0387953519
URL on the other hand, stands for Uniform Resource Locator. These are strings used to identify a resource as well as give information on how to access it. For example, http://www.jonlee.ca is a URL. It tells us that we can find the resource at www.jonlee.ca using the http protocol to access it. Other examples of URLs are:
- ftp://randomhost.com/directory/file.txt
- mailto:jon@jonlee.ca
- https://mail.google.com
So in fact, URLs are a subset of URIs. Every URL is a URI but not every URI is a URL. A URI like ISBN: 978-0387953519 tells us the resource is at 978-0387953519 and that it is an ISBN code but it does not tell us how to access it! This type of URI is known as an Uniform Resource Name (URN).
Confused? Maybe this diagram will explain it a little bit better. (I made it myself 
)
In 1994, it was decided that web addresses should be formally referred to as URI. URL was therefore a deprecated term but it had already gained so much popularity and widespread use that today, the two terms are practically synonymous. To be correct however, you should use the term URI (I’m currently trying to break the URL habit but it’s hard!).
Trivia: URI stood for Universal Resource Identifier until 1998 when the “U” was changed to stand for “Uniform”. However, in URL and URN, the “U” has always stood for “Uniform”.
Armed with this great knowledge, you can use it to impress your boss, girlfriend, boyfriend, teacher, mother … the possibilities are endless!
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Thank you for this post! I was actually wondering what the heck a URI was, thinking maybe I just didn’t see the L right, the I was supposed to be an L… hehe. But now I understand better.
Me, too. Thanks for this little lesson Jon!
That’s what I thought at first too! But I figured they wouldn’t let something like that slip through hundreds of releases..
Oooh.. well you learn something new everyday.
I just noticed the URI thing on wordpress today, and thought they might have forgotten to capitalize the L so it looks like URl
I searched Wikipedia, saw that they were different, but didn’t wanna read both pages.
This pretty much explained it in much less words… thanks
The first time I left a comment on someone’s blog, I left it blank because I didn’t know what that meant. But then I noticed my name didn’t link anywhere =P
That’s for that Jon! I’ve always wondered but never took the time to find out.
I think URIs still need to have a protocol, so /usr/bin/data.txt is not a URI but
file://usr/bin/data.txt is.
Well, well. I never knew this before! Thanks for the info!
[...] URI/URL – Uniform Resource Identifier/Locator [...]
Turning an ISBN into a URL is also possible: library://ISBN:1234124 tells you to invoke the “library” protocol (that is, charge into the local public library, bark orders at the librarians to bring you relevant books, reference materials, a Long Island Iced Tea and some biscuits. Not much different to HTTP, is it?).
Hi Jim. Photos i received. Thanks