Question

Explain the relationship between uniform resource locators (URLs) and uniform resource identifiers (URIs). Give an example of a URI that is not a URL.

Short answer

A URI is a way to identify a resource; a URL is a specific type of URI that locates a resource. Example of a non-URL URI: urn:isbn:0451450523.

Step-by-step solution

Define Uniform Resource Identifier (URI)

A URI (Uniform Resource Identifier) is a string of characters used to identify a resource over a network. It can be subdivided into a locator (URL), a name (URN), or both.

Define Uniform Resource Locator (URL)

A URL (Uniform Resource Locator) is a specific type of URI that not only identifies a resource but also provides information on how to locate it, usually including the protocol (e.g., http, https), and the address of the resource (e.g., www.example.com).

Discuss Relationship Between URL and URI

All URLs are URIs, but not all URIs are URLs. Essentially, a URL is a subset of a URI with the additional capability of locating a resource on the Internet. In essence, a URI is a way to identify a resource, and a URL is a way to identify and locate it.

Provide an Example of a URI That Is Not a URL

An example of a URI that is not a URL is a URN (Uniform Resource Name). URNs are used to identify resources by their name in a given namespace rather than by their location. Example: urn:isbn:0451450523.

Key concepts

Uniform Resource Identifier

A Uniform Resource Identifier (URI) is like an ID card for resources on a network. Think of it as a way to identify anything, be it a website, an email address, or even a book in a library. A URI is a string of characters that uniquely identifies a resource. It can be broken down into two main types: locators and names.

Types of URIs:

• URL (Uniform Resource Locator): This helps you not only to identify but also to find where exactly the resource lives on the network. It's like having a detailed address.
• URN (Uniform Resource Name): This simply gives the resource a specific name that is unique in a particular namespace, regardless of where it is located.

This means all URLs and URNs are types of URIs, but they serve different purposes.

Uniform Resource Locator

A Uniform Resource Locator (URL) is a specific type of URI. Its main job isn't just to identify a resource but also to locate it on the internet. When you think about a URL, think about how it includes exact information on where to find the resource.

Components of a URL:

• Protocol: Specifies the method used to access the resource (e.g., http, https, ftp).
• Address: This includes the domain name (e.g., www.example.com) and can also include a path to a specific resource within that domain.

So, while every URL is a URI, not every URI is a URL. URLs give us a way to both identify and locate a resource, which is why they're so common in our daily internet usage.

For example, in the URL https://www.example.com/page1:

• https:// is the protocol
• www.example.com is the domain name
• /page1 specifies the exact resource within that domain.

Uniform Resource Name

A Uniform Resource Name (URN) is another type of URI. Unlike URLs, URNs are used to identify a resource by its name in a specific namespace. They provide a persistent, location-independent resource identifier.

Example of a URN:

• urn:isbn:0451450523 - This URN identifies a book by its International Standard Book Number (ISBN), not by where you can find it.

URNs are useful when we want to refer to a resource without tying it to a particular location. For instance, digital books, scientific papers, and legal documents often use URNs to ensure that their identifier remains the same, no matter where the resource is moved.

So, while a URL is like a detailed address locating a resource online, a URN is more like a name given to a resource that stays the same regardless of where it is stored.