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Hack 23. Build Google Directory URLs

Use ODP category information to build URLs for the Google Directory.

The Google Directory ( overlays the Open Directory Project (ODP or DMOZ, ontology onto the Google core index. The result is a Yahoo!-like directory hierarchy of search results and their associated categories with the added magic of Google's popularity algorithms.

The ODP opens its entire database of listings to anybody—provided you're willing to download a 283 MB file (and that's compressed!). While you're probably not interested in all the individual listings, you might want particular ODP categories, or you may be interested in watching new listings flowing into certain categories.

Unfortunately, the ODP does not offer a way to search by keyword sites added within a recent time period. So instead of searching for recently added sites, the best way to get new site information from the ODP is to monitor categories.

Because the Google Directory builds its directory based on the ODP information, you can use the ODP category hierarchy information to generate Google Directory URLs. This hack searches the ODP category hierarchy information for keywords that you specify, and then builds Google Directory URLs and checks to make sure that they're active.

You'll need to download the category hierarchy information from the ODP to get this hack to work. The compressed file containing this information is available from, and the specific file is here: Before using it, you must uncompress it with a decompression application specific to your operating system. In the Unix environment, the command looks something like this:

% gunzip structure.rdf.u8.gz

Bear in mind that the full category hierarchy is over 35 MB. If you just want to experiment with the structure, you can get an excerpt from This version is a plain text file and does not require uncompressing.

2.5.1. The Code

Save the following code to a text file called



# Uses ODP category information to build URLs into the Google Directory.

# Usage: perl "keywords" < structure.rdf.u8


use strict;


use LWP::Simple;


# Turn off output buffering.



my $directory_url = "";


@ARGV == 1

  or die qq{usage: perl "{query}" < structure.rdf.u8\n};


# Grab those command-line specified keywords and build a regular expression.

my $keywords = shift @ARGV;

$keywords =~ s!\s+!\|!g;


# A place to store topics.

my %topics;


# Loop through the DMOZ category file, printing matching results.

while (<>) {

  /"(Top\/.*$keywords.*)"/i and !$topics{$1}++ 

    and print "$directory_url/$1\n";


2.5.2. Running the Hack

Run the script from the command line ["How to Run the Hacks" in the Preface], along with a query and the piped-in contents of the DMOZ category file:

% perl "keywords" < structure.rdf.u8

Replace keywords with the particular keywords that you're after.

If you're using the shorter category excerpt structure.example.txt, use this:

% perl "keywords" < structure.example.txt

2.5.3. The Results

Feeding the keyword mosaic into this hack would look something like this:

% perl "mosaic" < structure.rdf.u8


2.5.4. Hacking the Hack

There isn't much hacking that you can do to this hack; it's designed to take ODP data, create Google URLs, and verify those URLs. How well you can get this to work for you really depends on the types of search words that you choose.

Choose words that are more general. If you're interested in a particular state in the U.S., for example, choose the name of the state and major cities, but don't choose the name of a very small town or of the governor. Choose the name of a company but not of its CFO. A good rule of thumb is to choose the keywords that you might find as entry names in an encyclopedia or almanac. You can easily imagine finding a company name as an encyclopedia entry, but it's a rare CFO who could achieve the same.

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