Each data source will have different set of attributes supported, click desired Supported Data Sources.
The datasource contains a schema, which is an array of Column elements and/or Calculated Column elements.
Optionally you can also add a filter element.
For a comprehensive list of Supported Data Sources click here.
<Datasource><Schema><Column name="Source Column Name"/><CalculatedColumn name="Source Calculated Column Name" formula="CONCAT(a,b)" />...</Schema><Filter>filter condition</Filter></DataSource>