Each cell contains a coefficient that you multiply with the stat in question. There are a few things in there that aren't in the formula, such as "baseline DPS" and so on, but for pieces of armor, the formula should work. Just don't try to apply it to weapons.
An example of an item would be, for example, Belt of Seething Fury. It is plate, has 993 armor, 48 Strength, 37 Stamina, 38 Haste Rating. Multiply each of these values by the corresponding stat in the plate-classes, and you should find that the value for "Warrior - Arms&Fury" ends up on top, meaning that the item is best suited for that class. Items with the same iLevel and slot usually end up getting more or less the same 'value' no matter what type of item it is.
Unfortunately, I can't give you the links to our parser scripts; we have a script where you just type in the itemID and it pulls the information from Wowhead and does all the calculations on-the-fly and spits out the finished calculations, but this should give you a general idea of where we're going with things.
Since it's a guild implementation, some stats are weighted slightly differently. We want tanks to gear up faster than DPS-classes, so typical tank stats (Dodge, Parry, Shield Block, etc) are cheaper than they 'should' be.
Aye, I'm aiming for the reverse, I don't want to take an item and assign it to a specific spec. Instead, I want to take a spec and give them a list of items they would like to have. Trying to give them targets to aim for, specifically for 5-man runs, since there's so damn many to pick from it can be hard to decide where you need to go. So in the end it's likely that a nice piece of plate will list for both tanky and dps warriors, but not healy pallies.