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
Prepares a subdirectory named mailcross.d in the current working directory, and
populates it with empty subdirectories for exactly
size subsets.
"add
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
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
Shows a list of available filters/wrapper scripts which can
be selected.
"testsuite
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
Removes the named filter(s) from the directory
mailcross.d/filters so that they are not used in the simulation.
"testsuite
Invokes every selected filter on the datasets added previously, and
calculates misclassification rates.
"testsuite
Describes the scheduled simulations.
"testsuite
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.
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:
