Mailto

   This allows a URL to specify an RFC822 addr-spec mail address.  Note
   that use of % , for example as used in forming a gatewayed mail
   address, requires conversion to %25 in a URL.

News

   The news locators refer to either news group names or article message
   identifiers which must conform to the rules for a Message-Id of RFC
   1036 (Horton 1987).  A message identifier may be distinguished from a
   news group name by the presence of the commercial at "@" character.
   These rules imply that within an article, a reference to a news group
   or to another article will be a valid URL (in the partial form).

   A news URL may be dereferenced using NNTP (RFC 977, Kantor 1986)
   (The ARTICLE by message-id command ) or using any other protocol for
   the conveyance of usenet news articles, or by reference to a body of
   news articles already received.

   Note 1:

      Among URLs the "news" URLs are anomalous in that they are
      location-independent. They are unsuitable as URN candidates
      because the NNTP architecture relies on the expiry of articles and
      therefore a small number of articles being available at any time.
      When a news: URL is quoted, the assumption is that the reader will
      fetch the article or group from his or her local news host.  News
      host names are NOT part of news URLs.

   Note 2:

      An outstanding problem is that the message identifier is
      insufficient to allow the retrieval of an expired article, as no
      algorithm exists for deriving an archive site and file name.  The
      addition of the date and news group set to the article's URL would
      allow this if a directory existed of archive sites by news group.

      Suggested subject of study in conjunction with NNTP working group.
      Further extension possible may be to allow the naming of subject
      threads as addressable objects.

Telnet, rlogin, tn3270

   The use of URLs to represent interactive sessions is a convenient
   extension to their uses for objects.  This allows access to
   information systems which only provide an interactive service, and no
   information server.  As information within the service cannot be




 
RFC 1630                      URIs in WWW                      June 1994


   addressed individually or, in general, automatically retrieved, this
   is a less desirable, though currently common, solution.

URN

   The "Universal Resource Name" is currently (March 1993) under
   development in the IETF.  A requirements specification is in
   preparation. It currently looks as though it will be a short string
   suitable for encoding in URI syntax, for which case the "urn:" prefix
   is reserved.  The URN shall be encoded precisely as defined in the
   (future) URN standard, except in that:

      If the official description of the URN syntax includes any
      constant wrapper characters, then they shall not be omitted from
      the URI encoding of the URN;

      If the URN has a hierarchical nature, then the slash delimiter
      shall be used in the URI encoding;

      If the URN has a hierarchical nature, the most significant part
      shall be encoded on the left in the URI encoding;

      Any characters with reserved meanings in the URI syntax shall be
      escape encoded

   These rules of course apply to any URI scheme.  It is of course
   possible that the URN syntax will be chosen such that the URI
   encoding will be a 1-1 transcription.

   An example might be a name such as

         urn:/iana/dns/ch/cern/cn/techdoc/94/1642-3

   but the reader should refer to the latest URN drafts or
   specifications.

WAIS

   The current WAIS implementation public domain requires that a client
   know the "type" of a object prior to retrieval. This value is
   returned along with the internal object identifier in the search
   response. It has been encoded into the path part of the URL in order