First notice that category in the url table is set to be 11 characters long. This means you can use a valid character to keep track of categories. If you are going to keep a category tree of any size, then use the category editor from mnogosearch.org. Here's how it works.

You can use either the tag column or the category column in the url for the same thing. Or you can categorize a site in two different ways. For example you could keep track of sites that are owned by a certain company and then categorize them as well. You could use the tag option to keep of ownership and use the category option for categories. The category option goes the same for the tag option.

A category can be broken down any way you choose. But for it to work with the category editor you have to use two characters for each level. If you use the category editor you have the choice to use a hex number going from 0-F or a 36 base number going from 0-Z. Therefore a top-level category like 'Auto' would be 01. If it has a subcategory like 'Ford', then it would be 01 (the parent category) and then 'Ford' which we will give 01. Put those together and you get 0101. If 'Auto' had another subcategory named 'VW', then its id would be 01 because it belongs to the 'Ford' category and then 02 because it's the next category. So its id would be 0102. If VW had a sub category called 'Engine' then it's id would start at 01 again and it would get the 'VW' id 02 and 'Auto' id of 01, making it 010201.

If you want to search for sites under that category then you pass it cat=010201 in the url...so create a select box and give like this one:

<OPTION value="01">AUTO
<OPTION value="0101">Ford
and so on...