\newcommand\DSV{{\sc dsv}}
\newcommand\WWW{{\sc www}}
\documentstyle[a4]{article}
\begin{document}
\title{Properties of Electronic Texts for Classification Purposes as
Suggested by Users}
\author{Fredrik Kilander \\
IntFilter \\
Department of Computer and Systems Sciences \\
Stockholm University \\
Electrum 230, S-164 40 Kista, Sweden \\
fk@dsv.su.se}
\maketitle

\section{Introduction}

Students at the Department of Computer and Systems Sciencs (\DSV) were
given the task of writing a short essay on the problem of using
machine learning to classify electronic texts and messages such as
electronic mail (email), Usenet News postings or World Wide Web (\WWW)
pages. For the more than one-hundred students the essay was a small
part of a wider examination. Fifty-four of them elected to adress the
issue.

This paper summarizes the student's suggestions and opinions as real
users of email, News and \WWW. The purpose is to collect information
from real users on what they perceive to be important properties in
electronic messages. This is in turn motivated by the long-term goal
of the IntFilter project at \DSV\ to classify electronic texts guided
by user-supplied examples.

\section{The Authors}

The authors of the essays were all students at \DSV, at the time
halfway through their second year of a four year curriculum. With all
likelyhood, all of them used \WWW\ and email at \DSV, some of them
also Usenet News. A non-neglible fraction indicated in their essays
experiences from working in other environments where email played an
important role. The majority of the authors were 20--30 years
old. Female authors provided nine of the essays.

\section{The Essays}

\begin{table}
\centering
\begin{tabular}{|l|r|} \hline
Keywords		&	40	\\
Sender			&	37	\\
Subject			&	30	\\
Length			&	21	\\
Date and time		&	21	\\
Categories of senders	&	13	\\
Recipients		&	11	\\
Relations to other texts &	9	\\
Semantic text analysis	&	6	\\
Readability analysis	&	6	\\
Keyword synonyms	&	5	\\
Attachments		&	5	\\
Language		&	4	\\
Priority		&	3	\\
Newsgroup		&	3	\\
Layout			&	2	\\
Negative keywords	&	2	\\
Author's keywords	&	1	\\
Nof readers		&	1	\\
History of sender	&	1	\\
\hline
\end{tabular}
\caption{\label{summary}Summary of suggested properties}
\end{table}

Table \ref{summary} shows a summary of the properties suggested by the
students. Most of them had approached the task with email in mind and listed
the sender first, followed by the subject. This likely reflects the
way most people peruse their mail. Many also noted keywords in the
body of the message as an important property, but as an afterthought
or after having spent time thinking further about the problem.
The appreciation of length appeared to be a very individual issue:
some authors apparently used length in conjunction with the sender to
hypothesize the contents of the message (again, mostly for mail).
Time was also an important factor for many; essentially the discussion
revolved around deadlines, events and the time a message was allowed
to be stored but not read.

\subsection{Sender (37)}

Although more students listed keywords as an important property, most
of those who noted the origin of a message did so first. This
indicates that this property was foremost in their minds when they set
about to tackle the problem. The concept of the sender was developed
in several ways:
\begin{itemize}
\item Senders can be persons, organizations or mechanisms.
\item Senders have properties.
\item Senders can be categorized.
\end{itemize}

Senders that are persons are usually known to the user. If not known
personally the social and organizational relation between the sender and
the user is often already established: supervisor, co-worker,
employee, client, customer etc. If the sending person is not known in
this manner, certain information can be imputed from the organization
behind the sender's adress. The domain adress symbolizes the company
or university and lends credibility, suspicion or anonymity to the
sender. In various degree this raises expectations about the contents
and importance of the message.

The contents from senders that are organizations or mechanisms are
usually more predictable: advertisements, regular subscriptions or
mailing-lists has a known level of commitment for the user. They
appear to carry the same distinctions in email as the morning paper
and the monthly bill does for paper mail.

\subsubsection{Categories of senders (13)}

Several authors indicated that senders should be categorized for
easier processing. Some recurring examples of such categories included
{\em friends, clients, co-workers, providers of vital information} and
{\em bosses}. Some authors recognized that the categories could
overlap (your boss can also be your friend) in which case other
mechanisms would have to be employed in order to determine which {\em
role} the sender is having in the message. 
% Apparently the sender's
% role affects the final importance of the message.

\subsubsection{History of sender (1)}

One author mentioned that the {\em history} of a sender is an
important property. This is quite natural considering that one learns to
expect a certain amount of quality, quantity and content from each
persistent source.

\subsection{Recipients (11)}

A number of authors felt that knowing the group of recipients of a
message was important. For email, the group was defined as the immediate
receivers and those who had received carbon-copies or were included in
a chain of forwardings. Knowing that others have recieved a message
influences several factors. Each user may be a member of several
groups (social or organizational). As a member of a particular group
each user can infer or hypothesize about the sender's expectations, ie
the {\em role} and level of commitment expected of the receiver. In
practical terms one is usually more inclined to answer a question
recieved only by oneself, than one put to a group. In the group anyone
can answer the question and some members may be uniqely qualified.

Mailing-lists and news define their groups explicitly by topic.
In the case of news, messages crossposted to other groups
was taken as an indication of content that spanned several
interestgroups.

One author noted that the number of readers of a message was
important.  This is used on the \WWW\ to estimate the popularity of
certain pages. It is an insecure measurement, however, in that it
doesn't reveal how many of the reader's that liked what they
got. Also, good pages does not get read automatically (except by
web-spiders), they must be fetched on demand.

\subsection{Subject (37)}

Many authors felt that the subject line was very important and
eschewed that it be searched for keywords or phrases. Some authors
recognized that subject lines can be useful, but also devastating if
their import is overly emphasized. Writing a good subject or title is
difficult and sometimes willfully abused.

Some author remarked that captions and subheadings were important
properties of the overall text. This is recognized on the \WWW\ where
such entities can be easily examined through the {\sc html} markup.


\subsection{Keywords (40)}

Almost all authors suggested that the classification of the message
should be aided by a keyword search. Several speculated that each user
could have a keyword list for each specific topic. Two writers noted
that keywords could be negative, ie not allowed in a matching
text. The lists were to be built manually, interactively from
user-supplied examples or completely automatically in the style of a
learning apprentice system.

One writer held that keywords supplied by the author (sender) should
be treated with greater emphasis.

\subsection{Keyword synonyms (5)}

Some authors noted that the search for relevant keywords could be
enhanced by using a dictionary of synonyms. It should be noted that
the benefit of such a dictionary is greatest when there is a number of
disassociated queries to answer, eg in an information retrieval
system. If individual users create their own lists of keywords for
specialized topics information in the dictionary is transferred into
each list. The list then becomes, if you like, a micro-dictionary for
each topic. A centralized dictionary is even more of value if it is
capable of providing matches on word stems as well as synonyms.

\subsubsection{Language (4)}

Four authors recognized the distinction created by different languages
and the possible confusion that could arise when keyword search did not
take the language of the text into consideration. Further, the user is
usually limited to a few languages and may take special interest in
messages written in a particular language.

\subsubsection{Readability analysis (6)}

Six authors felt that a surface analysis of the readability of the
message would be of value. Such analysis is usually based on the
number of long words, the average number of words per sentence and
perhaps the presence of certain idiom and phrases. The analysis
results in some index indicating the required reading effort.

\subsubsection{Semantic text analysis (6)}

A few authors felt that the {\em meaning} of the text could not be
disregarded and suggested that natural language methods be employed.


\subsection{Length (21)}

Length was quoted by many authors as important for categorization but
the opinions on its interpretation varied, apparently from their
personal experiences. The basic import of a message's length was that
a longer message would take more time to read. Some authors argued
that short messages usually were the result of errors or test and
could therefore mostly be ignored, while others felt that the sender
and subject determined the importance of short messages.

One interesting argument was that the length of the text could not be
used alone to estimate the time needed to read the message. Length
should be used in conjunction with readability analysis in that a
short, difficult message may cause the user substantial more effort
than a longer, more easily assimilated message.

One author used the personal heuristic that very long messages from
particular senders consisted not text at all but of embedded
binaries. The willingness to accept long messages could also be
dependent on practical circumstance, for instance when using a dial-up
communication line and a slow modem.

None of the authors suggested that the proportion between cited and
original text was an important property, but neither did any one
specify explicitly that length was should be counted only as original
content.


\subsection{Date and time (21)}

Information about dates and times were considered to be important by
many authors. Several suggested that important time information could
be embedded within the message and should be identified and
extracted. Surprisingly enough, some were apparently ready to discard
messages about events past without reading them.

At least one author suggested that unread email should be
subject to aging, ie receive higher priority with time. This implies
that a sorting mechanism other than arrival time is in operation. 


\subsection{Relations to other texts (9)}

A message sent in reply to a question was regarded as important. The
impact on the desire to read the message was of course dependent on
the context: most users are presumably interested in answers to their
own questions, and less impressed by information they already have. As
a side note, this is one of the reasons for the development of
Frequently Asked Questions (FAQ) in mailinglists and news; experienced
readers tire of seeing the same questions being raised and answered
over and over again.

A few authors noted that the subject line sometimes acts as an
indication of relationship between news postings; the string {\em Re:}
is usually prepended to a followup and may in some cases be the only
indication that the text was prompted by another. The Internet message
header has a field for a {\em References:} relation but this is
occasionally empty due to faulty software or inexperienced users.

Some authors also noted that tails of long threads were usually less
interesting as the debate usually diverted from the original
subject or degraded into nit-picking between factions.


\subsection{Attachments (5)}

Five authors remarked that the type and quantity of attachments to a {\sc
mime}-type message could help in the classification of the
message's importance.


\subsection{Priority (3)}

Some authors had evidently been in contact with other mail-systems
where explicit priority could be assigned by the sender. This appears
to be an obvious source of information but just like many other
properties affixed by the sender it is not safe from abuse.

\subsection{Layout (2)}

Two authors placed emphasis on the layout of the message. The layout
gives information about the nature of the message; if its written in
haste of after careful editing. The authors may have had \WWW-pages
in mind, and while not a layout language, {\sc html} markup gives a
lot of information about the expected appearance of the page.

\section{Final comments}

A number of authors suggested that a combination of techniques and
properties should be used for classification. Considering that many of
the authors wrote with their personal experience in mind, it should be
safe to say that people use whatever information they have at hand and
form heuristics around that. For example, most email clients display the
sender, the subject and the length of the message. It is therefore not
surprising that these properties are mentioned so frequeuntly in the
essays. Similarly, no-one appears to have used keyword search to sort
their email, but it is a convenient way to find information in news
archives and on the \WWW. 

On a more general level, the attention given to email by the authors
appears guided by two things, the commitment expected of them and
crucial time information, ie deadlines. Commitment is not easily
quantified, but many cite a letter from their ``boss'' as an example
of something which is given the highest priority. It may be possible
to model the expected commitment using categories of senders and
receivers.

In order to pursue computer-aided classification of email, one could
allow the user to formalize his or hers personal heuristics in the
email client, in the form of simple rules. Like one author suggested,
the rules would not have to be internally consistent, and each
rule is allowed to vote on each message. The sum of the votes is the
final classification.

\end{document}
