with filtering software, or by entering URLs one by one into the  URL checker  that most

filtering software companies provide on their Web sites.  Filtering software companies

will entertain requests for recategorization from proprietors of Web sites that discover

their sites are blocked.  Because new pages are constantly being added to the Web,

filtering companies provide their customers with periodic updates of category lists.  Once

a particular Web page or site is categorized, however, filtering companies generally do

not re review the contents of that page or site unless they receive a request to do so, even

though the content on individual Web pages and sites changes frequently.  

2.  The Methods that Filtering Companies Use to Compile Category Lists

While the way in which filtering programs operate is conceptually straightforward

  by comparing a requested URL to a previously compiled list of URLs and blocking

access to the content at that URL if it appears on the list   accurately compiling and

categorizing URLs to form the category lists is a more complex process that is impossible

to conduct with any high degree of accuracy.  The specific methods that filtering software

companies use to compile and categorize control lists are, like the lists themselves,

proprietary information.  We will therefore set forth only general information on the

various types of methods that all filtering companies deposed in this case use, and the

sources of error that are at once inherent in those methods and unavoidable given the

current architecture of the Internet and the current state of the art in automated

classification systems.  We base our understanding of these methods largely on the

detailed testimony and expert report of Dr. Geoffrey Nunberg, which we credit.  The

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