URI vs. URL: Understanding the Difference Between Identifiers and Locators

Clarify the distinction between URI (Uniform Resource Identifier) and URL (Uniform Resource Locator). This guide explains their definitions, how they differ in terms of resource identification and location specification, and their roles in accessing online resources.

URI vs. URL: Understanding the Difference

Introduction

URI (Uniform Resource Identifier) and URL (Uniform Resource Locator) are terms frequently used in web development and networking. While often used interchangeably, they have distinct meanings. This article clarifies their differences.

What is a URI?

A URI is a string of characters that identifies a resource on the internet. It can specify the resource's location, its name, or both. There are two main types of URIs:

  • URL (Uniform Resource Locator): Specifies the location of a resource.
  • URN (Uniform Resource Name): Specifies the name of a resource.

URI Syntax

The general syntax of a URI is:

scheme:[//authority]path[?query][#fragment]
  • scheme: The protocol (e.g., http, https, ftp, mailto).
  • authority: (Optional) Includes the hostname, port, and potentially username/password.
  • path: The path to the resource on the server.
  • query: (Optional) Additional data, often used to pass parameters.
  • fragment: (Optional) Specifies a section within a resource (e.g., a specific part of a web page).

URI Examples:

  • mailto:someone@example.com
  • urn:oasis:names:specification:docbook:dtd:xml:4.1.2

What is a URL?

A URL is a *type* of URI that specifies the location of a resource on the internet. It's the address you type into your web browser to access a web page, image, or other online content.

URL Syntax

The syntax of a URL is the same as the general URI syntax.

Key Parts of a URL:

  • Scheme: Protocol (http or https).
  • Authority: Domain name (www.example.com) and port number (optional).
  • Path: Location of the resource on the server (/page/index.html).
  • Query String: Parameters (?param1=value1&param2=value2).
  • Fragment: Reference to a specific section within the resource (#section1).

Key Differences: URI vs. URL

Feature URI URL
Meaning Uniform Resource Identifier (identifies a resource) Uniform Resource Locator (locates a resource)
Scope Broader; includes URLs and URNs Subset of URI; only locates resources
Identification Identifies by name or location or both Identifies by location only

Examples:

  • URI: urn:isbn:0-476-27557-4 (identifies a book by its ISBN but doesn't give its location)
  • URL: https://www.example.com (gives the location of a web page)

Conclusion

In essence, a URI is a general way to identify a resource. A URL is a specific type of URI that tells you where to find that resource on the internet. All URLs are URIs, but not all URIs are URLs.