title: How does the ActiveRecord pattern differ from the Domain Object or Data Mapper pattern?
body: <p>I was looking at <a href="http://datamapper.org/" rel="noreferrer">DataMapper</a>, which appeared at first glance to use the ActiveRecord ORM pattern.  Other people said that it uses the DataMapper and/or the Domain Object pattern.  </p>
  
  <p>What is the difference between those patterns?  </p>