Re: mid and cid URLs

Al Gilman (
Tue, 21 Nov 1995 16:42:47 -0500 (EST)

From: (Al Gilman)
Message-Id: <>
Subject: Re: mid and cid URLs
To: (Ned Freed)
Date: Tue, 21 Nov 1995 16:42:47 -0500 (EST)
Cc:, elevinso@Accurate.COM,,
In-Reply-To: <01HXWLFACL0G9BWNBV@INNOSOFT.COM> from "Ned Freed" at Nov 21, 95 12:03:24 pm

To follow up on what Ned Freed said ...
  <Al Gilman:>
  > 1. By construction, these two nominal schemes are one scheme and we
  > should only use one name for them.  MID or MIDCID are possibles.
  While its certainly possible to do this, I don't see why you'd want to.
  Message-IDs and Content-IDs are distinct entities. A given part of a message
  can have neither, one, or both of them.
I thought from Ed's construction that one was expected to cite a
Message-ID to reference a Content-ID.  So I didn't expect that
one would not find an identified [part] Content in an
un-identified Message.

  There is also the question of scope. I see support of message-ids as a
  cross-message sort of thing, preferably implemented as an index emcompassing
  the entire mailbox. (Preference would be given to whatever message is
  "current", of course.) Content-ids, on the other hand, 
  are largely intended to
  be used within a single message. It therefore seems logical to give some
  indication of scope in the scheme identifier.

Defining a URI scheme gets you into a much bigger market than
that.  Look at what Hypermail does to link things up from a
combination of Message-IDs, mailbox designations, and http: URLs.

If any significant traffic in CID-identified parts develops,
people will want to refer to them across wider scopes.  In
particular, I would expect that enclosures to one message will be
recycled as references cited [or attached as a
message/external-body] in other messages.  You only discover
after the fact that there are seven people who would be
interested in what you cooked up to tell Joe.

  I guess what I'm asking is what advantage you in collapsing the schemes into
  one. If there is a big one I guess I wouldn't mind making such a change.
If you wrote the code in a Web Browser that parses URIs, would you 
want to add a special case for a "cid:" scheme that you would never,
in practice, see?  Now, that's a small hit.  But what you are 
registering as a URI scheme is something a lot of people handle.
MIME implementors are not the only people affected.