CREATE TABLE user_activities (
  id serial primary key not null,
  target_id integer not null, -- location_id, comment_id, stories_id
  target varchar not null, -- locations, comments
  action varchar not null, -- "comments on some stories with id, submmited a locations, submitted a stories"
  link text,
  comment text,
  created_at timestamp default(now()) not null,
  updated_at timestamp default(now()) not null
)