Re: mid and cid URLs

Al Gilman (
Tue, 21 Nov 1995 17:17:48 -0500 (EST)

From: (Al Gilman)
Message-Id: <>
Subject: Re: mid and cid URLs
To: (Keith Moore)
Date: Tue, 21 Nov 1995 17:17:48 -0500 (EST)
Cc:,, elevinso@Accurate.COM,
In-Reply-To: <> from "Keith Moore" at Nov 21, 95 03:35:12 pm

To follow up on what Keith Moore said ...
  I've been thinking of "cid", "message/external-body; access-type=cid"
  (and by association, "mid") as *URL* schemes, especially (for the
  former two) within the context of multipart/related.  Such a scheme is
  useful even without the URN infrastructure.
For all the reasons that Ned has been teaching me, a "cid" does
not represent a reliable _location_ reference.  It is a name used
in searching for the cited object.  Even inside the same MIME

The Message-ID is in use today as an object name in the
"In-reply-to" header in RFC 822 mail that knows nothing about
MIME.  And it is now used by Hypermail at random _receiving_
sites that have nothing to do with the sending location to
reconstruct threads of dialog.

The Message-ID is a URN that is successful today.  Content-ID is
[?? you tell me.].

You don't have to define and provide a retrieval service for object
naming on widely-distributed objects like RFC 822 mail and News to
be a useful construct.