Underwriter uses SQLite to store tag information. The database structure
is based off of the ["Toxi"][1] schema.

[1]: http://howto.philippkeller.com/2005/04/24/Tags-Database-schemas/

The three tables used are

* `cards`, containing the name and creation date
* `tags`, containing an ID of the tag and the name
* `tagmap`, where each row matches a card with a tag

The `tagmap` is many-to-many. For instance, if `X` is a member of
`cards`, and `Y`, `Z` are members of tags, then `(X,Y)` and
`(X,Z)` can be members of `tagmap`.