title: Class diagram for ad system
body: <p>So I created an class diagram according to the assignment, is this the right way to do it ? I am especially not sure about the <code>Column class</code> because it seems to me that it can be just variable.</p>
  
  <blockquote>
    <p>You are building application that will load data from several
    different advertising systems and then store the data into database,
    so it will be possible to analyze them.</p>
    
    <p>You need to take in mind that every advertising system has different
    structure of report: Different named columns, different order of
    columns, different date formats Also data from ad systems are in
    different data formats(JSON,CSV,XML),</p>
    
    <p>Reports from each system contains different amount of columns, our
    application is interested only in some of them: date, ad_campaing,
    ad_group, keyword, impressions, price (in every system they have
    different name)</p>
    
    <p>Logic of advertising accounts is that one ad campaing contains
    multiple ad groups and one ad group contains multiple keywords.</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/bM8hc.png" rel="nofollow"><img src="https://i.stack.imgur.com/bM8hc.png" alt="enter image description here"></a></p>