Exactly, I dont mean to beat a dead horse, but most bog standard web apps have the quoted items in a db anyway, and these are very common problems.
For example if we have a few tables we can determine which menu items a user could eat:
users
user_ingredient_exclusions
ingredients
menu_ingredients
menu
-- items a user can eat based on not having any items in the excluded list
select distinct m.*
from menu m
inner join menu_ingredients mi on m.id = mi.menu_id
left join user_ingredient_exclusions e on e.ingredient_id = mi.ingredient_id
inner join user u on u.id = e.user_id
where e.id is null
and u.id = @id
