A Uniform Resource Identifier (URI) is a string of characters used to identify a resource. A resource can be anything that may have to be referred to: a physical document (e.g. stored within a file), a folder, some logical that is produced on-the-fly or even some user task. A URI is not the resource itself but just a way to designate this resource. The resource itself may not be aware of its own URI and several URIs may refer to the same resource.