[4][a] URLs occur most commonly to reference web pages (HTTP/HTTPS) but are also used for file transfer (FTP), email (mailto), database access (JDBC), and many other applications.
Uniform Resource Locators were defined in RFC 1738 in 1994 by Tim Berners-Lee, the inventor of the World Wide Web, and the URI working group of the Internet Engineering Task Force (IETF),[7] as an outcome of collaboration started at the IETF Living Documents birds of a feather session in 1992.
[7][8] The format combines the pre-existing system of domain names (created in 1985) with file path syntax, where slashes are used to separate directory and filenames.
Conventions already existed where server names could be prefixed to complete file paths, preceded by a double slash (//).
[10] Early WorldWideWeb collaborators including Berners-Lee originally proposed the use of UDIs: Universal Document Identifiers.
[13]: §3 The authority component consists of subcomponents: This is represented in a syntax diagram as: The URI comprises: A web browser will usually dereference a URL by performing an HTTP request to the specified host, by default on port number 80.