How some filters work

[KAREN SCHNEIDER]

Some filters work by blocking hostnames.  At least one product
(X-stop) claims to block ONLY by hostname, including full files
(http://www.foobird.com/sexyfoo.gif).  We're still gathering filter
feature info (and in fact the TIFAP project isn't focusing on  filter
features yet, since we're in the question-testing phase; it will be
easier to describe how most of these filters work after they've
been tested a couple of weeks).  However, you could say, very
broadly,  and this is very tentative,  that many first-generation
filters block primarily by keyword, and newer filters block
primarily by combination or by hostnames alone (in addition to
blocking or unblocking by protocol, time/place/manner, etc.,
depending on the product).   This is not to say that one is better
than the other; I think it's a bit of a red herring to focus on
keyword vs. hostname.  If you can't access what you need, and
stuff you don't want gets through, then the product is not
performing as advertised, regardless of how it functions. If you
do not have diagnostic and corrective tools--e.g. if you cannot
determine how the product works, or correct its errors in
"judgment" in a real-time environment--then this further impacts
performance.  How do filters perform?  Well, we'll see.  ;-)


Karen G. Schneider/schneider.karen at epamail.epa.gov
Contractor, GCI/Director, US EPA Region 2 Library
http://www.epa.gov/Region2/library/
TIFAP: http://www.bluehighways.com/tifap/