A content-id URL scheme

Ed Levinson (elevinso@Accurate.COM)
Fri, 03 Feb 1995 16:29:35 -0500

Message-Id: <9502032130.AA07352@Accurate.COM>
To: uri@bunyip.com
Subject: A content-id URL scheme
Date: Fri, 03 Feb 1995 16:29:35 -0500
From: Ed Levinson <elevinso@Accurate.COM>


Attached is an internet-draft describing a URL scheme for MIME
content-ids.  Given that it's brief, 3 pages, I've taken the liberty of
distributing it to this list and I solicit your comments.


Content-Description: <draft-levinson-cid-00.txt>

       Network Working Group                            E. Levinson
       Internet Draft: URL:cid                  ACCURATE Info. Sys.
       <draft-levinson-cid-00.txt>                 January 31, 1995

               CID: The Content-ID Uniform Resource Locator

       This draft document is being circulated for comment.  Please
       send your comments to the authors or to the uri-wg mail list
       <uri-wg@bunyip.com>.  If consensus is reached, this URL may
       be registered as a scheme with IANA and this document may be
       submitted to the RFC editor as an Informational protocol

       Status of this Memo

       This document is an Internet Draft; Internet Drafts are
       working documents of the Internet Engineering Task Force
       (IETF) its Areas, and Working Groups.  Note that other
       groups may also distribute working documents as Internet

       Internet Drafts are draft documents valid for a maximum of
       six months.  They may be updated, replaced, or obsoleted by
       other documents at any time.  It is not appropriate to use
       Internet Drafts as reference material or to cite them other
       than as a "working draft" or  "work in progress".

       Please check the abstract listing in each Internet Draft
       directory for the current status of this or any other
       Internet Draft.


       The Uniform Resource Locator (URL) scheme, "cid", allows
       compound or aggregate objects in a multipart mail message to
       refer to one another by their body part labels.

       1. Introduction

       Consider an object that consists of a set of distinct parts
       containing internal references to one another.  The
       structure of such references will be called an entity
       structure after [SGML].  Within a given computing system,
       the entity structure usually exists as file references.
       When transferring the object between systems, the sending
       system's file names may be problematic because of special
       characters or differing interpretations of those characters.

       The encapsulation of these objects within [MIME] requires
       preserving the entity structure while providing a neutral
       representation for the references.  A Content-ID Uniform
       Resource Locator (cid URL) serves that purpose.

       A companion document, [REL], contains an example of cid

       Levinson                 Expires July 31, 1995                  [Page 1]
       Internet Draft                                           URL Scheme: cid


       2. CID

       RFC1738 [URL] reserves the scheme "cid" for Content-ID.
       This memorandum defines the syntax for the cid URL.

       A cid URL takes the form

               cidurl     = "cid" ":" cid-spec

       where cid-spec is a restricted form of "addr-spec" as
       defined in [RFC822].  The purpose of the restriction is to
       eliminate special characters from the cid URL.  Such
       characters can be problematical in many environments (e.g.,
       HTML and SGML) in which the cid URL may be used.  Cid URLs
       are a subset of MIME content-IDs and RFC822 message-IDs

               cid-spec   = local-part "@" host ; globally unique

               local-part = atom                ; as per RFC822

               domain-ref = atom                ; as per RFC822

               host       =                     ; RFC1738, sec 3.1

       A cid differs from a MIME content-id in the ommission of the
       leading and trailing brackets, "<" and ">", and the
       restricted character set.  To transform a cid into a valid
       content-id, surround the cid-spec with the enclosing
       brackets, i.e.,

               content-id = "<" cid-spec ">".

       Cids are globally unique [MIME, p.19].  A common technique
       for generating them is to use a time and date stamp with the
       local host's domain name, e.g., 950124.162336@XIson.com.

       3. Security

       Security issues are not addressed in this memorandum.

       4. References

       [822]       Crocker, D., Standard for the Format of ARPA Internet Text
                   Messages, August 1982, University of Delaware, RFC 822.

       [MIME]      Borenstein, N. and Freed, N., MIME (Multipurpose Internet
                   Mail Extensions): Mechanisms for Specifying and Describing
                   the Format of Internet Message Bodies, June 1992, RFC 1341.

       [REL]       Alvestrand, H. T., Levinson, E., The MIME Multipart/Related
                   Content-Type, work in progress,

       Levinson                 Expires July 31, 1995                  [Page 2]
       Internet Draft                                           URL Scheme: cid


       [SGML]      ISO 8879:1988, Information processing -- Text and office
                   systems -- Standard Generalized Markup Language (SGML).

       [URL]       Berners-Lee, T., Masinter, L., and McCahill, M., Uniform
                   Resource Locators (URL), December 1994, RFC 1738.

       5. Acknowledgements

       This work reflects the ideas freely provided to the author by many peo-
       ple, including Tim Berners-Lee who pointed me at the idea of using a URL
       "scheme" in the SGML encapsulation proposal.

       6. Author's Address

       Edward Levinson
       Accurate Information Systems, Inc.
       2 Industrial Way
       Eatontown, NJ  07724-2265
       +1 908 389 5550

       Levinson                 Expires July 31, 1995                  [Page 3]