The relationship and difference between URL, URI and URN

URL

Uniform Resource Locator (URL) is a reference to a resource and a method of accessing it. It is commonly known as the URL, which is in the address bar of the browser.

A URL consists of the following different parts:

• Protocol: usually https or http, a method of telling the browser or device how to access resources. Of course, there are other protocols, such as ftp, mailto, etc.
• Next is ://
• Hostname: A registered name (domain name) or IP address that represents an IP address, a numeric identifier used to identify a device connected to a network.
• The port number, preceded by a colon:
• Path: can refer to a file system path, usually used as a code segment
• Parameters: optional query parameters starting with a question mark, where multiple parameters are connected with &
• Hash: used to provide quick links to titles on a page, such as anchor links

URI

Similar to URL, Uniform Resource Identifier (URI) provides a method to identify resources. However, unlike URL, URI does not provide a method to locate the resource.

The most common form of URI is the Uniform Resource Locator (URL), often specified informally as a web address. From this, it can be seen that URI is a superset of URL, and every URL is essentially a URI.

URN

Uniform Resource Name (URN) is the historical name of Uniform Resource Identifier (URI), and URN is used as the URI scheme.

From the perspective of a set, URN and URL are both subsets of URI, as shown in the figure:

Taking a website as an example, the following clearly shows the contents of URI, URN, and URL, which can more intuitively reflect the relationship between the three:

To conceptually summarize the relationship between the three, as shown in the figure:

picture