I'm learning DB design.  How would you change the following schema which tries to replicate Stack Overflow's functionality:create_table questions, :force => true do |t|    t.text      question,         :null => false    t.text      description,  :null => false    t.integer       up_votes,         :null => false, :default => 0    t.integer       down_votes,       :null => false, :default => 0  t.timestampsendcreate_table answers, :force => true do |t|    t.integer       question_id,  :null => false    t.text      answer,               :null => false    t.integer       up_votes,         :null => false, :default => 0    t.integer       down_votes,       :null => false, :default => 0  t.timestampsendcreate_table question_comments, :force => true do |t|    t.integer   question_id,  :null => false    t.text      comment,          :null => false  t.timestampsendcreate_table answer_comments, :force => true do |t|    t.integer   answer_id,    :null => false    t.text      comment,      :null => false  t.timestampsendcreate_table tags, :force => true do |t|    t.string        tag,  :null => false, :limit => 100  t.timestampsendadd_index tags, [tag], :name => tag_UNIQUE, :unique => truecreate_table question_tags, :force => true do |t|  t.integer     question_id,  :null => false  t.integer     tag_id,               :null => false  t.timestampsendcreate_table users, :force => true do |t|    t.string        first_name,   :limit => 45,       :null => false    t.string        last_name,    :limit => 45,       :null => false    t.string        email,            :limit => 100,  :null => false    t.string        password,                                     :null => false    t.string        salt,                                             :null => false  t.timestampsendcreate_table user_votes, :force => true do |t|    t.integer       user_id,  :null => false    t.integer       question_id    t.integer       answer_id    t.boolean       is_positive_vote    t.timestampsendcreate_table user_favorites, :force => true do |t|    t.integer       user_id,  :null => false    t.integer       question_id    t.integer       answer_id    t.timestampsendcreate_table question_flags, :force => true do |t|    t.integer       user_id,  :null => false    t.integer       question_id    t.timestampsendcreate_table answer_flags, :force => true do |t|    t.integer       user_id,  :null => false    t.integer       question_id    t.timestampsendcreate_table related_questions, :force => true do |t|    t.integer       question_id,                  :null => false    t.integer       related_question_id,  :null => false    t.timestampsend
Critique my Stack Overflow schema
ruby;ruby on rails