Subject: Re: revised 822, and Reference: fields, etc.

From: Jacob Palme <[email-masked]>
Date: Wed, 24 Nov 1999 23:52:05 +0100

At 16.57 +0000 99-11-24, Hugh Sasse wrote:
> One concern I have is that there is no recommended upper limit for
> In-Reply-To: and Reference: message-id lists.  If a conversation continues
> for a long time then it seems to me that these fields could grow to be
> very large, possibly longer than the message bodies. I wonder if a token
> to say "this list has been truncated" would be useful, to stop these
> getting ridiculously big, whilest acknowledging they have been trimmed?
> It might be something like an ellipsis (...) at the end of the field.

The accepted method, although not specified in the MSGFORMAT document,
is to truncate in the middle, and ensure that the first and the last
element in the References: header is not truncated.

I made statistics on an early mail system 15 years ago, and got the
following result:

     This table shows the number of threads of different sizes for
     letters (column 2-4) and conference entries (column 5-7).

     Number of    Threads with personal   Threads with group
     texts in     letters of this size    entries of this size
     the thread   abso-  per-    cumula-  abso-  per-    cumula-
                  lute   cent    tive     lute   cent    tive

     1            3079   43.3 %   43.3 %  1436   43.4 %   43.4 %
     2            2206   31.0 %   74.3 %   633   19.1 %   62.5 %
     3-4          1253   17.6 %   91.9 %   611   18.5 %   81.0 %
     5-7           438    6.2 %   98.0 %   316    9.6 %   90.6 %

     8-10           94    1.3 %   99.4 %   121    3.7 %   94.2 %
     11-13          25    0.4 %   99.7 %    53    1.6 %   95.8 %
     14-16           5    0.1 %   99.8 %    34    1.0 %   96.9 %
     17-20          12    0.2 %  100.0 %    34    1.0 %   97.9 %

     21-25           3    0.0 %  100.0 %    14    0.4 %   98.3 %
     26-30           0    0.0 %  100.0 %    14    0.4 %   98.7 %
     31-50           0    0.0 %  100.0 %    26    0.8 %   99.5 %
     51-             0    0.0 %  100.0 %    16    0.5 %  100.0 %

     Total        7115  100.0 %           3308  100.0 %

                    For personal messages   For group entires

     Median number of messa-
     ges in a thread            2             2

     Lower quartile             1             1

     Upper quartile             3             4

     Excluding entries without any comment on them (only including trees
     with more than one entry in them):

     Median number of messa-
     ges in a thread            2             3

     Lower quartile             2             2

     Upper quartile             3             5

Note: By thread in the statistics above is meant the number of messages
in the entire tree structure, not just in one path from top to bottom
from the tree structure. This, with

                +----A----+
                |         |
                B         D

The thread length was counted as 3, not as 2.

The full report on my statistics can be found at
URL in RTF format: http://dsv.su.se/jpalme/reports/c10166.rtf
URL in Adobe Acrobat format: http://dsv.su.se/jpalme/reports/c10166.pdf

(In that paper, the word "comment tree" is used for what today is
usually named a "thread". I think "comment tree" is a better way,
since it is a three structure, not a single path as the word "thread"
seems to indicate.)
------------------------------------------------------------------------
Jacob Palme <[email-masked]> (Stockholm University and KTH)
for more info see URL: http://www.dsv.su.se/jpalme/