I'm aware of the WoW add-on programming community, but what I can find no documentation on is any API for accessing WoW's databases from the web. I see third-party sites like WoWHeroes.com and Wowhead use game data (item and character databases,) so I know it's possible. But, I can't figure out where to begin. Is there a web service I can use or are they doing some sort of under-the-hood work that requires running the WoW client in their server environment?
Sites like Wowhead and WoWHearoes use client run addons from players which collect data. The data is then posted to their website. There is no way to access WoW's database. Your best bet is to hit the armory and extract the XML returned from your searches. The armory is just an xml transform on xml data returned.