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An idea for MID and CID URsomethings

From: <Harald.T.Alvestrand@uninett.no>
Date: Sun, 23 Jul 1995 22:08:52 +0200
Message-Id: <199507232008.WAA00170@dale.uninett.no>
To: drums@cs.utk.edu, ietf-822@dimacs.rutgers.edu, uri@bunyip.com
I talked to some people briefly about this during IETF.
Since it points out some problems with "what does an ID identify"
in both MIME and RFC 822, I think "drums" may be a nice "home list"
to discuss it on; I've set reply-to accordingly.

I don't know whether it is either best or appropriate for me to
continue editing this; does anyone feel like taking responsibility?
(Ed Levinson had a previous document on CID URLs, but I've lost my
copy of it, and he seems to have shelved the idea for the moment)


         Harald A

draft                      MID and CID URLs                    July 95

                      Message-ID and Content-ID URLs

                     Sun Jul 23 19:16:56 MET DST 1995

                         Harald Tveit Alvestrand

    Status of this Memo

    This document specifies two classes of URsomethings, MID and CID.
    The intention is to allow reference to messages and message
    components using a syntax that looks much like that used for URLs
    in the Web.

    This draft document is being circulated for comment.  Please send
    comments to the author, or to.....

    The following text is required by the Internet-draft rules:

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

    Internet Drafts are draft documents valid for a maximum of six
    months. Internet Drafts 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 I-D abstract listing contained in each Internet
    Draft directory to learn the current status of this or any other
    Internet Draft.

    The file name of this version is draft-alvestrand-not-submitted-

Alvestrand                  Expires Jan 96                    [Page 1]
draft                      MID and CID URLs                    July 95

    1.  Introduction

    When writing information resources, it would sometimes be nice to
    have a reasonably unique way of referring to mail and news

    In some cases, like when you are sending a message coded in HTML,
    it is also nice to be able to refer to parts of a message by

    These references are not Uniform Resource Locators, since they do
    not encode the location of their objects, neither are they Uniform
    Resource Names, since they do not fulfil all requirements of RFC
    1737; for lack of a better idea, I call them Reasonably Unique
    Identifying Names; this term obviously does not have a four-letter

    2.  The Message-ID UR?

    2.1.  Syntax   The syntax of the message-ID locator is

    mid = "mid:" message-id

    where message-id is imported from STD 12, "Internet Mail", RFC
    822.  When it is used in protocols which do not allow the full
    character set of RFC 822, it must be encoded using the

    2.2.  The identified object

    The message-ID locator resolves to an Internet message.

    This identifies a message header and a message body conformant to
    RFC 822 and (possibly) MIME; due to the history of Internet
    messages, the following differences must be expected between
    different copies of the same message:

     (1)   Variable number of "Received:" lines in the header

     (2)   Randomized order of other header lines

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draft                      MID and CID URLs                    July 95

     (3)   Addition of "Resent-*" headers

     (4)   Addition/subtraction of other non-standard headers like "X-
           Listproc-version", "Old-Received" or "PP-Warning"

     (5)   Changes of content-transfer-encoding for MIME messages

     (6)   Changes of wrapping for multiline headers

    An object is still considered the same object after undergoing
    these changes.

    The following changes may arise because of errors or misfeatures
    that are known to occur in Internet mailers, but represent
    erroneous representations of the message:

     (1)   Changes to, addition of or removal of standard headers like
           "To:", "Subject:" or "Content-type:"

     (2)   Substituting tabs for spaces or vice versa

     (3)   Adding or deleting blank lines at the end of the message

     (4)   Breaking of lines without using a MIME content-transfer-

    2.3.  Resolution

    No specific resolution mechanism is defined by this document.

    Possible resolution mechanisms include:

     (1)   Searching through a database of MIDs for messages seen at
           this UA

     (2)   Searching publicly accessible message archives for messages
           with this MID

     (3)   Sending mail to the author of the referencing document to
           ask which message he intended to point to

Alvestrand                  Expires Jan 96                    [Page 3]
draft                      MID and CID URLs                    July 95

    3.  The Content-ID UR?

    3.1.  Syntax

    cidref = "cid:" content-id

    where content-ID is imported from RFC 1541 (MIME).  Percent
    encoding must be used when the cid is used in a protocol that does
    not allow the full set of CID characters.

    3.2.  The identified object

    The CID references a MIME entity, consisting of headers and body.

    The following changes can be applied to a CID-referenced object
    without considering the object to be different:

     (1)   Change of content-transfer-encoding, including recoding of

     (2)   Addition or deletion of headers that do not begin with
           "content-"; this is necessary to allow the existence of two
           messages with the same content-id, but with different
           message headers (These should naturally have different

    3.3.  Resolution

    The same resolution mechanisms as for message-ids can be applied
    to cids.

    4.  Security considerations

    Security issues are not consiered in this memo.


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draft                      MID and CID URLs                    July 95

         Here is the title of the reference

Alvestrand                  Expires Jan 96                    [Page 5]
Received on Monday, 24 July 1995 03:19:49 UTC

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