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dbacl: Is It Working?

Laird A. Breyer


dbacl is a UNIX/POSIX command line toolset which can be used in scripts to classify a single email among one or more previously learned categories.

This document is intended to help you check that your installation of dbacl is working as it should. When trying out new software, there are many things to learn and things that can go wrong, and because dbacl is a statistical tool, it can sometimes be surprising and unpredictable. When you get unexpected results, is it because dbacl doesn't work as claimed, an undiscovered bug, problems to do with learning, problems in your scripts? Knowing what to look for is half the battle.

In the text below, some commands are written after a '%'. The '%' represents your shell prompt, and you are expected to enter the commands following it. If a line doesn't start with a '%', then it represents what you are likely to see as command output.

The basics

Let's first see if dbacl is properly installed on your system. At the shell prompt, type:

% dbacl -V
dbacl version 1.11
Copyright (c) 2002,2003,2004,2005 L.A. Breyer. All rights reserved.
dbacl comes with ABSOLUTELY NO WARRANTY, and is licensed
to you under the terms of the GNU General Public License.
If you get something that looks like this, then you know that dbacl is installed and ready to use. If the shell can't find the command dbacl, then you most likely need to download and install the program, as explained in the next section. If you get an error, you need to install the program first (read the next section). If you've built the program from sources yourself and your shell still can't find dbacl, then you need to indicate the full path to the program each time.

Installation time

Since dbacl is an open source (GPL) program, you are likely to first encounter it in one of two forms: a source code form as a compressed tar file named something like dbacl-1.11.tar.gz, or a preinstalled binary form that comes with your GNU/Linux or other operating system.

In the source code form you are expected to first build the program in the usual way:

% tar xfz dbacl-1.11.tar.gz
% cd dbacl-1.11
% ./configure && make
If something goes wrong during the build, you will see an error message and the build will not finish. Troubleshooting the build is beyond the scope of this document, so let's assume it finished without errors.

How do we know that the freshly built programs operate correctly? We run some standard tests:

% make check
All 55 tests passed

This command produces a lot of output on your terminal, but the important line is the one indicating whether all tests have passed. Normally, when dbacl is packaged, all the test are guaranteed to pass, but small differences between computer systems can cause failures. By running "make check" you will know if things are working on your system. If you see a failure, it is most likely that some error message during the build steps will point to some difficulties which you can fix.

On some systems, it is possible that a handful of tests will fail because the configure script cannot find a suitable Unicode environment. In that case, the error output contains "nbsp;" tokens which could not be converted to spaces. This is harmless.

Finally, you must install the freshly built programs in the correct location on your system. The simplest way is to type as root:

% make install-strip

If your version of dbacl was preinstalled on your operating system, then you do not need to build the programs from source, and you cannot "make check" to see if the tests passed. However, you can normally trust the distributor of your operating system and assume that all the build tests were successful.

Sanity checks

There are two simple ways to check that dbacl works correctly. The first way is to read the tutorials and type yourself the commands given there. The tutorials and where to find them are listed in the dbacl man page, which you can read by typing

% man dbacl
You should expect to see nearly identical output as described in the tutorials.

The second way to check that dbacl works is to run a small classification test with your own email collections. This is a better test because it gives you confidence that the system will work for you. Below is just a quick explanation, the full details can be read by typing

% man mailcross

You will need two mbox files containing collected emails of two different types. The types could be spam and notspam, or anything else, but make sure that the two mbox files do not have messages in common and represent different topics. There should also be roughly the same number of messages in each. Now type the following (you can replace spam and notspam by any names you like):

% mailcross prepare 5
% mailcross add spam /path/to/spam.mbox
% mailcross add notspam /path/to/notspam.mbox
% mailcross learn
% mailcross run
% mailcross summarize

These commands could take a while depending on how big your mbox files are. The summary is a table which shows the number of errors in the experiment, which consists in learning some random subsets of the spam.mbox and notspam.mbox files and trying to predict the remaining messages. If all went well, you should expect the number of errors to be less than 10%, but the exact percentage depends on how many messages you have, how easy to separate they are, and the default switches used by the test system.

Don't forget to clean up the mailcross temporary directory by typing

% mailcross clean

Particular symptoms

If you've tried the things above and you still suspect things aren't working correctly, here is a small list of symptoms and their likely causes.

dbacl seems to forget what it learns
You keep feeding data to dbacl for learning, but it seems to forget everything very soon. This symptom occurs because dbacl truly does forget data. Unlike certain other spam filters, dbacl doesn't support incremental learning. You must teach it everything in one go. You can simulate incremental learning by keeping and growing a collection of training examples, and periodically teaching dbacl the full collection.