form of trial and error, a system is given a  training set  consisting of documents

preclassified into two or more groups, along with a set of features that might be

potentially useful in classifying the sets.  The system then  learns  rules that assign

weights to those features according to how well they work in classification, and assigns

each new document to a category with a certain probability.  

Notwithstanding their  artificial intelligence  description, automated text

classification systems are unable to grasp many distinctions between types of content that

would be obvious to a human.  And of critical importance, no presently conceivable

technology can make the judgments necessary to determine whether a visual depiction fits

the legal definitions of obscenity, child pornography, or harmful to minors.  

Finally, all the filtering software companies deposed in this case use some form of

human review in their process of winnowing and categorizing Web pages, although one

company admitted to categorizing some Web pages without any human review

. 

SmartFilter states that  the final categorization of every Web site is done by a human

reviewer.   Another filtering company asserts that of the 10,000 to 30,000 Web pages that

enter the  work queue  to be categorized each day, two to three percent of those are

automatically categorized by their PornByRef system (which only applies to materials

classified in the pornography category), and the remainder are categorized by human

review.   SurfControl also states that no URL is ever added to its database without human

review.  

Human review of Web pages has the advantage of allowing more nuanced, if not

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