A Uniform Resource Name (URN) is a specific type of Uniform Resource Identifier (URI) used to identify resources on the internet. Unlike URLs, which specify a specific network address or location, URNs identify resources regardless of their current location.

A URN consists of two main components: a namespace identifier and a specific identifier. The namespace identifier identifies the namespace to which the resource belongs, while the specific identifier within that namespace uniquely identifies the resource.

URNs are intended to provide a persistent and unique identification of resources, regardless of changes in location or availability of the resource on the internet. They are used, for example, for identifying scientific publications, standards, digital library resources, and other resources.

A URI (Uniform Resource Identifier) is a string used to uniquely identify a resource on the Internet or another network. A URI is used to locate or identify a specific resource, whether it's a web page, a file, an image, a video, or any other type of resource.

A URI can be divided into different parts:

1. URL (Uniform Resource Locator): A specific type of URI used to identify the address of a resource and the mechanism for accessing it. URLs typically include a protocol (such as HTTP or FTP), hostname, port (optional), path, and query string.

2. URN (Uniform Resource Name): A URN is another type of URI used to identify a resource by its name permanently, regardless of its current location or how it is accessed. A well-known example of a URN is the ISBN system for books.

URI is a more general term that encompasses both URLs and URNs. It is an important component of the internet and is used in many applications to access and identify resources.

A URL (Uniform Resource Locator) is a string used to uniquely identify and locate the address of a resource on the Internet or another network. A URL typically consists of several parts that specify various information about the resource:

1. Protocol: The protocol specifies how the resource should be accessed or transferred. Common protocols include HTTP (Hypertext Transfer Protocol), HTTPS (HTTP Secure), FTP (File Transfer Protocol), and FTPS (FTP Secure).

2. Hostname: The hostname identifies the server where the resource is hosted. This can be a domain like "example.com" or an IP address indicating the exact location of the server.

3. Port (optional): The port is a numerical address on the server that allows access to specific services. Default ports are often used implicitly (e.g., port 80 for HTTP), but custom ports can also be specified for special services.

4. Path: The path specifies the location of the resource on the server. It can refer to a specific directory or file.

5. Query string (optional): The query string is used to pass additional parameters to the server that can be used to identify or customize the requested resource. The query string starts with a question mark and usually contains a series of key-value pairs separated by the ampersand (&).

Together, these parts of a URL form the complete address of a resource on the Internet or another network. URLs are used in web browsers, hyperlinks, APIs, and other internet applications to access and identify resources.