HTML Uniform Resource Locators
A Uniform Resource Locator (URL), commonly called a web address, is a reference to a web resource which specifies its location on a computer network and a mechanism for restoring it. A URL is a special type of Uniform Resource Identifier (URI), although sometimes these two terms are used interchangeably. In most web browsers, the URL of a web page is displayed above the page in an address bar.
A URL can be composed of words or an Internet Protocol (IP) address. Generally, users enter the name as they are easier to remember than numbers.
The syntax of a full Web address is the following:
|scheme||Specifies the type of Internet service. http/https is the most common.|
|prefix||Specifies a domain prefix. www is the default for http.|
|domain||Specifies the name of the Internet domain.|
|port||Specifies the port number at the host. 80 is the default for http.|
|path||Specifies a path at the server. If it is omitted, the resource will be located at the root directory.|
|filename||Specifies the name of a resource or document.|
In HTML, a URL can have a partial form which is often called a relative URL. To create a full URL, a browser fills in missing parts of the URL from the relevant parts of the URL of the current page.
The following table lists some common schemes:
|http (HyperText Transfer Protocol)||Common web pages (non encrypted).|
|https (Secure HyperText Transfer Protocol)||Secure web pages (encrypted).|
|ftp (File Transfer Protocol)||Downloading or uploading files.|
|file||A file on your computer.|
URLs can be transmitted over the Internet only using the ASCII character set. If a URL has characters outside the ASCII set, the URL must be converted.
Non-ASCII characters are replaced with a "%", which is followed by hexadecimal digits.
URLs cannot contain spaces. URL encoding commonly replaces a space with %20, or a plus (+) sign.