What are URI and URL?

In this interconnected world of ours, we constantly interact with web addresses. They are a crucial part of the Internet, allowing us to visit specific pages online. You might already be aware that these web addresses are sometimes referred to as URLs. However, there is another term that is sometimes used interchangeably with URL. That term is “URI,” and despite how similar it sounds to a URL, they are not the same thing! This similarity sometimes confounds people, so we are here to clarify it all! Read on to learn all there is about URIs and URLs!

This post includes:

• What is a URI?
• What is a URL?

What is a URI?

URI stands for Uniform Resource Identifier. It is a sequence of characters used to identify resources on and offline. In other words, a URI’s purpose is to point to a specific website, file, or piece of data. So, when you open a picture online, your browser uses a specific URI to fetch it.

There is not much else to say about the raw definition of URI. A good real-world equivalent is street names and numbers. They are used in the same way to identify a specific building, the same way a URI points to a particular resource online. In the same way, streets have names and numbers, a URI consists of a few elements.

• Scheme - The scheme is the first part of the URI, and it defines the protocol used to establish the connection (https, ftp, mailto, etc.);
• Authority - This part shows who controls the resource we are looking for. “Control,” in this sense, means who hosts the resource. This part itself can consist of a few elements;
• Host - You must specify the host in a URI. It can be either a domain name or an IP address, but it is mandatory;
• User Info - An optional part that is used for authentication in older systems. Most modern URIs do not actually contain this information for security reasons;
• Port - Another optional part, which can be used when the default port for the connection is not available or the host uses a different one;
• Path - A path is required in order for a resource to be reachable on or offline;
• Query String - Sometimes you might need to specify additional parameters (APIs tend to do this), so this goes after the pat, separated from it by a question mark (?);
• Fragment - The final section of a URI, a fragment is used to point to a specific part of the resource. It is used for in-page navigation. For example, pointing to a specific heading in a blog post. Fragments begin with a hashtag (#).

To put it all together, here is a typical URI.

https://www.fastcomet.com/kb/what-is-a-cms#benefits-of-using-a-cms

The scheme is https:, separated from the authority by two slashes. Then you have the authority, which is www.fastcomet.com. Afterwards, you have the path to the resource: /kb/what-is-a-cms. Finally, the fragment which points to a specific heading in the document: #benefits-of-using-a-cms.

Now, you might think that the URI looks a lot like a URL, which is the other thing we mentioned at the beginning of this article. You are not wrong because–as the old saying goes–every URL is a URI, but not every URI is a URL. We might have modernized it a bit.

However, there is another type of URI that is not used to locate a resource online. It is the URN (Uniform Resource Name). Despite its ominous abbreviation, it is nothing more than an identifier for a specific resource. You cannot follow them to find the online resource, though, as they are nothing more than static, unchanging identifiers. Typically, URNs are used to search for items in a database, which is why they are not as widely used by the everyday Internet-goer.

Here is a quick example of what a URN can look like: urn:isbn:0451450523. According to its ISBN (International Standard Book Number), this particular one identifies a book in a database. You cannot find the book online with it, but a bookstore might use such a URN to see if they have a book available in their database.

With that said, we should also discuss the most prominent URI online: the URL.

What is a URL?

You can understand now why people sometimes use URI and URL interchangeably. A URL (Uniform Resource Locator) is the other type of URI that exists online. However, unlike the URN, it identifies the resource and offers a way to locate it. However, as we mentioned earlier, not all URIs are URLs, so you should not confuse the two terms.

Put simply, a  URL is the string of characters you put in your browser’s bar to go to a website. Take our previous example again:

https://www.fastcomet.com/kb/what-is-a-cms#benefits-of-using-a-cms

It will take you to the “Benefits of Using a CMS” heading of our knowledge base article about what a Content Management System is. As you can see, it not only identifies the resource (the article) but provides a direct link to it, which means you can open it in your browser and peruse it. A URN cannot do that.

Once you write the URL in your browser’s address bar, your browser follows the typical DNS steps to locate the resource. Then, depending on the outcome of the request, it shows you the resource or any errors that the host might return, such as 404 Not Found, if the host does not have the resource you are looking for.

That is all there is to say about URIs and URLs. The term URI is the broad term used to identify resources on the Internet, whereas a URL is a specific URI that also locates. They are similar; however, they are not the same.

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