URLs

A URL is an identifier that points to an electronically accessible resource, such as a directory file on a machine in a network, or a document stored in a database.

URLs appear in the format scheme:scheme_information.

We can represent a scheme as HTTP, FTP, file, or another term that identifies the type of resource and the mechanism by which we can access the resource.

In a web browser location or address box, a URL for a file available using HyperText Transfer Protocol (HTTP) starts with http:. An example is http://www.ibm.com. Files available using File Transfer Protocol (FTP) start with ftp:. Files available locally start with file:.

The scheme_information commonly identifies the Internet machine making a resource available, the path to that resource, and the resource name. The scheme_information for HTTP, FTP and file generally starts with two slashes (//), then provides the Internet address separated from the resource path name with one slash (/). For example,

http://www.ibm.com/software/webservers/appserv/library.html.

For HTTP and FTP, the path name ends in a slash when the URL points to a directory. In such cases, the server generally returns the default index for the directory.