NAME
mailcross - a cross-validation simulator for use with dbacl.
SYNOPSIS
mailcross command [ command_arguments ]
DESCRIPTION
mailcross automates the task of cross-validating email filtering and
classification programs such as dbacl(1). Given a set of categorized
documents, mailcross initiates simulation runs to estimate the
classification errors and thereby permits fine tuning of the parameters
of the classifier.
Cross-validation is a method which is widely used to compare the
quality of classification and learning algorithms, and as such permits
rudimentary comparisons between those classifiers which make use of
dbacl(1) and bayesol(1), and other competing classifiers.
The mechanics of cross-validation are as follows: A set of pre-
classified email messages is first split into a number of roughly
equal-sized subsets. For each subset, the filter (by default,
dbacl(1)) is used to classify each message within this subset, based
upon having learned the categories from the remaining subsets. The
resulting classification errors are then averaged over all subsets.
The results obtained by cross validation essentially do not depend upon
the ordering of the sample emails. Other methods (see
mailtoe(1),mailfoot(1)) attempt to capture the behaviour of
classification errors over time.
mailcross uses the environment variables MAILCROSS_LEARNER and
MAILCROSS_FILTER when executing, which permits the cross-validation of
arbitrary filters, provided these satisfy the compatibility conditions
stated in the ENVIRONMENT section below.
For convenience, mailcross implements a testsuite framework with
predefined wrappers for several open source classifiers. This permits
the direct comparison of dbacl(1) with competing classifiers on the
same set of email samples. See the USAGE section below.
During preparation, mailcross builds a subdirectory named mailcross.d
in the current working directory. All needed calculations are
performed inside this subdirectory.
EXIT STATUS
mailcross returns 0 on success, 1 if a problem occurred.
COMMANDS
prepare size
Prepares a subdirectory named mailcross.d in the current working
directory, and populates it with empty subdirectories for
exactly size subsets.
add category [FILE]...
Takes a set of emails from either FILE if specified, or STDIN,
and associates them with category. All emails are distributed
randomly into the subdirectories of mailcross.d for later use.
For each category, this command can be repeated several times,
but should be executed at least once.
clean Deletes the directory mailcross.d and all its contents.
learn For every previously built subset of email messages, pre-learns
all the categories based on the contents of all the subsets
except this one. The command_arguments are passed to
MAILCROSS_LEARNER.
run For every previously built subset of email messages, performs
the classification based upon the pre-learned categories
associated with all but this subset. The command_arguments are
passed to MAILCROSS_FILTER.
summarize
Prints statistics for the latest cross-validation run.
review truecat predcat
Scans the last run statistics and extracts all the messages
which belong to category truecat but have been classified into
category predcat. The extracted messages are copied to the
directory mailcross.d/review for perusal.
testsuite list
Shows a list of available filters/wrapper scripts which can be
selected.
testsuite select [FILTER]...
Prepares the filter(s) named FILTER to be used for simulation.
The filter name is the name of a wrapper script located in the
directory /usr/share/dbacl/testsuite. Each filter has a rigid
interface documented below, and the act of selecting it copies
it to the mailcross.d/filters directory. Only filters located
there are used in the simulations.
testsuite deselect [FILTER]...
Removes the named filter(s) from the directory
mailcross.d/filters so that they are not used in the simulation.
testsuite run
Invokes every selected filter on the datasets added previously,
and calculates misclassification rates.
testsuite status
Describes the scheduled simulations.
testsuite summarize
Shows the cross validation results for all filters. Only makes
sense after the run command.
USAGE
The normal usage pattern is the following: first, you should separate
your email collection into several categories (manually or otherwise).
Each category should be associated with one or more folders, but each
folder should not contain more than one category. Next, you should
decide how many subsets to use, say 10. Note that too many subsets
will slow down the calculations rapidly. Now you can type
% mailcross prepare 10
Next, for every category, you must add every folder associated with
this category. Suppose you have three categories named spam, work, and
play, which are associated with the mbox files spam.mbox, work.mbox,
and play.mbox respectively. You would type
% mailcross add spam spam.mbox
% mailcross add work work.mbox
% mailcross add play play.mbox
You can now perform as many simulations as desired. Every cross
validation consists of a learning, a running and a summarizing stage.
These operations are performed on the classifier specified in the
MAILCROSS_FILTER and MAILCROSS_LEARNER variables. By setting these
variables appropriately, you can compare classification performance as
you vary the command line options of your classifier(s).
% mailcross learn
% mailcross run
% mailcross summarize
The testsuite commands are designed to simplify the above steps and
allow comparison of a wide range of email classifiers, including but
not limited to dbacl. Classifiers are supported through wrapper
scripts, which are located in the /usr/share/dbacl/testsuite directory.
The first stage when using the testsuite is deciding which classifiers
to compare. You can view a list of available wrappers by typing:
% mailcross testsuite list
Note that the wrapper scripts are NOT the actual email classifiers,
which must be installed separately by your system administrator or
otherwise. Once this is done, you can select one or more wrappers for
the simulation by typing, for example:
% mailcross testsuite select dbaclA ifile
If some of the selected classifiers cannot be found on the system, they
are not selected. Note also that some wrappers can have hard-coded
category names, e.g. if the classifier only supports binary
classification. Heed the warning messages.
It remains only to run the simulation. Beware, this can take a long
time (several hours depending on the classifier).
% mailcross testsuite run
% mailcross testsuite summarize
Once you are all done with simulations, you can delete the working
files, log files etc. by typing
% mailcross clean
The progress of the cross validation is written silently in various log
files which are located in the mailcross.d/log directory. Check these
in case of problems.
SCRIPT INTERFACE
mailcross testsuite takes care of learning and classifying your
prepared email corpora for each selected classifier. Since classifiers
have widely varying interfaces, this is only possible by wrapping those
interfaces individually into a standard form which can be used by
mailcross testsuite.
Each wrapper script is a command line tool which accepts a single
command followed by zero or more optional arguments, in the standard
form:
wrapper command [argument]...
Each wrapper script also makes use of STDIN and STDOUT in a well
defined way. If no behaviour is described, then no output or input
should be used. The possible commands are described below:
filter In this case, a single email is expected on STDIN, and a list of
category filenames is expected in $2, $3, etc. The script writes
the category name corresponding to the input email on STDOUT. No
trailing newline is required or expected.
learn In this case, a standard mbox stream is expected on STDIN, while
a suitable category file name is expected in $2. No output is
written to STDOUT.
clean In this case, a directory is expected in $2, which is examined
for old database information. If any old databases are found,
they are purged or reset. No output is written to STDOUT.
describe
IN this case, a single line of text is written to STDOUT,
describing the filter’s functionality. The line should be kept
short to prevent line wrapping on a terminal.
bootstrap
In this case, a directory is expected in $2. The wrapper script
first checks for the existence of its associated classifier, and
other prerequisites. If the check is successful, then the
wrapper is cloned into the supplied directory. A courtesy
notification should be given on STDOUT to express success or
failure. It is also permissible to give longer descriptions
caveats.
toe Used by mailtoe(1).
foot Used by mailfoot(1).
ENVIRONMENT
Right after loading, mailcross reads the hidden file .mailcrossrc in
the $HOME directory, if it exists, so this would be a good place to
define custom values for environment variables.
MAILCROSS_FILTER
This variable contains a shell command to be executed repeatedly
during the running stage. The command should accept an email
message on STDIN and output a resulting category name. It should
also accept a list of category file names on the command line.
If undefined, mailcross uses the default value
MAILCROSS_FILTER="dbacl -T email -T xml -v" (and also magically
adds the -c option before each category).
MAILCROSS_LEARNER
This variable contains a shell command to be executed repeatedly
during the learning stage. The command should accept a mbox type
stream of emails on STDIN for learning, and the file name of the
category on the command line. If undefined, mailcross uses the
default value MAILCROSS_LEARNER="dbacl -H 19 -T email -T xml
-l".
TEMPDIR
This directory is exported for the benefit of wrapper scripts.
Scripts which need to create temporary files should place them a
the location given in TEMPDIR.
NOTES
The subdirectory mailcross.d can grow quite large. It contains a full
copy of the training corpora, as well as learning files for size times
all the added categories, and various log files.
WARNING
Cross-validation is a widely used, but ad-hoc statistical procedure,
completely unrelated to Bayesian theory, and subject to controversy.
Use this at your own risk.
SOURCE
The source code for the latest version of this program is available at
the following locations:
http://www.lbreyer.com/gpl.html
http://dbacl.sourceforge.net
AUTHOR
Laird A. Breyer <laird@lbreyer.com>
SEE ALSO
bayesol(1) dbacl(1), mailinspect(1), mailtoe(1), mailfoot(1), regex(7)