In some cases, URLs are used to locate resources that contain
   pointers to other resources. In some cases, those pointers are
   represented as relative links where the expression of the location of
   the second resource is in terms of "in the same place as this one
   except with the following relative path". Relative links are not
   described in this document. However, the use of relative links
   depends on the original URL containing a hierarchical structure
   against which the relative link is based.

   Some URL schemes (such as the ftp, http, and file schemes) contain
   names that can be considered hierarchical; the components of the
   hierarchy are separated by "/".














 
RFC 1738            Uniform Resource Locators (URL)        December 1994


3. Specific Schemes

   The mapping for some existing standard and experimental protocols is
   outlined in the BNF syntax definition.  Notes on particular protocols
   follow. The schemes covered are:

   ftp                     File Transfer protocol
   http                    Hypertext Transfer Protocol
   gopher                  The Gopher protocol
   mailto                  Electronic mail address
   news                    USENET news
   nntp                    USENET news using NNTP access
   telnet                  Reference to interactive sessions
   wais                    Wide Area Information Servers
   file                    Host-specific file names
   prospero                Prospero Directory Service

   Other schemes may be specified by future specifications. Section 4 of
   this document describes how new schemes may be registered, and lists
   some scheme names that are under development.

3.1. Common Internet Scheme Syntax

   While the syntax for the rest of the URL may vary depending on the
   particular scheme selected, URL schemes that involve the direct use
   of an IP-based protocol to a specified host on the Internet use a
   common syntax for the scheme-specific data:

        //:@:/

   Some or all of the parts ":@", ":",
   ":", and "/" may be excluded.  The scheme specific
   data start with a double slash "//" to indicate that it complies with
   the common Internet scheme syntax. The different components obey the
   following rules:

    user
        An optional user name. Some schemes (e.g., ftp) allow the
        specification of a user name.

    password
        An optional password. If present, it follows the user
        name separated from it by a colon.

   The user name (and password), if present, are followed by a
   commercial at-sign "@". Within the user and password field, any ":",
   "@", or "/" must be encoded.





 
RFC 1738            Uniform Resource Locators (URL)        December 1994


   Note that an empty user name or password is different than no user
   name or password; there is no way to specify a password without
   specifying a user name. E.g., <URL:ftp://@host.com/> has an empty
   user name and no password, <URL:ftp://host.com/> has no user name,
   while <URL:ftp://foo:@host.com/> has a user name of "foo" and an
   empty password.

    host
        The fully qualified domain name of a network host, or its IP
        address as a set of four decimal digit groups separated by
        ".". Fully qualified domain names take the form as described
        in Section 3.5 of RFC 1034 [13] and Section 2.1 of RFC 1123
        [5]: a sequence of domain labels separated by ".", each domain
        label starting and ending with an alphanumerical character and