urn vs url vs uri

Firstly, know that:
- URLs are a type of URI
- URNs are a type of URI
- URCs are a type of URI
- etc..

---
URI 
 - a standard for identifying documents using a short string of numbers, 
letters, and symbols.
 - defined by https://datatracker.ietf.org/doc/html/rfc3986
 
Examples:
  - URLs
  - URNs
  - URCs
  - ...
 
--- 
URL
 - Contains information about how to fetch a resource from its location.
 - Always start with the protocol
 - Can be relative

Examples:
 - http://example.com/mypage.html
 - file:///home/user/file.txt
 - tel:1-888-555-5555
 
--- 
URN
 - Identifies a resource by a unique and persistent name, but doesn't necessarily tell you how to locate it on the internet. 
 - It usually starts with the prefix urn:

Examples:
 - urn:isbn:0451450523 to identify a book by its ISBN number.
 - urn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66 a globally unique identifier
 
--- 
URC
 - Points to meta data about a document rather than to the document itself. 
An example of a URC is one that points to the HTML source code of a page

Examples:
 - like: view-source:http://example.com/