A URI for an e-mail - mailto:firstname.lastname@example.org - is structured differently from one for a graphic on a web page or from one for a file transfer - ftp:/dokumente/smtp.txt. The objects identified in the Uniform Resource Identifier can be a text file or a graphic, an Excel file, an audio or video sequence. Each individual object has its own unique Uniform Resource Identifier. The URI is identified by the protocol - http, mailto, ftp, gopher, news - by the service such as World Wide Web(WWW) and by a valid address.
A Uniform Resource Identifier or Universal Resource Identifier can be a Uniform Resource Locator( URL) or a Uniform Resource Name( URN). It identifies specific content on the Web: a sound file, a video file, an image document, or a text document. The terms URI and URL are used interchangeably. A session ID can be appended to the URI identifier to identify sessions.