Getting Data For Add-ons

[Æris]

Ok this is probably a total Noob question, but I'm trying to figure out exactly how you get the data needed for add-ons. For example, if say I wanted to create an add-on that told you what quest an item was attached to and who to turn it into (such as for Rep. Quests); do I have to construct a database from scratch or can I query the server for the information?

In either case, what is the best way of going about and creating such a database?