Whats the differences between XPATH and Database?

1.When i use list widget or data grid,  i can select from xpath or database as datasource. They seems has very similar function,  what’s the exact difference?   2. when use a dropdown filter on list view,   i can also select Xpath or database on filter option item. What’s the difference?    They must match with list view’s datasource type?  
1 answers
  1. Database only allows constraints per attribute. Xpath allows you to add more elaborate constraints to the retrieve command, not only per attribute but also over association.
  2. Same difference as 1