Uniform Resource Identifier

URI syntax diagram

Uniform Resource Identifier (URI) is a string of characters used to identify a resource on the Internet. It enables the identification of resources available over the network, such as web pages, images, and services, by location, name, or both. The concept of URIs is a fundamental component of the World Wide Web and is standardized by the Internet Engineering Task Force (IETF) in RFC 3986.

Overview

A URI provides a simple and extensible means for identifying a resource. It encompasses both Uniform Resource Locators (URLs), which are locators (addresses) of resources, and Uniform Resource Names (URNs), which are names for resources. While all URLs and URNs are URIs, not all URIs are URLs or URNs. The distinction lies in the fact that URLs describe the address at which a resource can be found, including the protocol required to retrieve it (e.g., HTTP, FTP), while URNs define a resource's identity in a namespace, independent of where it is located.

Syntax

The syntax of a URI is defined in RFC 3986. A URI consists of several components, some of which may be optional, depending on the type of URI. The general syntax is:

   scheme:[//[user:password@]host[:port]][/]path[?query][#fragment]

- Scheme: Indicates the protocol to be used to access the resource (e.g., http, https, ftp). - User:Password: Optional credentials for accessing the resource. - Host: The domain name or IP address of the server hosting the resource. - Port: Optional port number if the service is running on a non-default port. - Path: The specific path to the resource on the server. - Query: Optional query parameters for accessing the resource. - Fragment: An optional fragment identifier for referring to a subsection of the resource.

Usage

URIs are used extensively on the Internet to locate and access resources. They are the foundation of web browsing, allowing web browsers to retrieve web pages, images, and other content from web servers. URIs are also used in many other contexts, such as in XML namespaces, to identify namespaces uniquely.

Encoding

Special characters in a URI must be percent-encoded to ensure they are correctly interpreted by web servers and clients. This involves replacing the character with a '%' followed by two hexadecimal digits representing the character's ASCII code. For example, spaces in a URI are replaced with '%20'.

Standardization

The standardization of URIs is crucial for ensuring interoperability across different systems and applications on the Internet. The IETF's RFC 3986 is the current standard that defines the syntax and semantics of URIs.

See Also

• Uniform Resource Locator
• Uniform Resource Name
• Internet Engineering Task Force
• World Wide Web

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