URL components

Every URL begins with the scheme by which a resource should be located. This specifies the transport mechanism, or location type, that should be used to find what you're looking for. There is a finite list of universally valid schemes that you can specify, including http, ftp, and even file for locally hosted resources. The scheme is always followed by a colon (:) delimiter. After the scheme specification, a URL could contain an optional authority specification, which itself contains a small handful of sub-components.