Explain the decision support system concept and how it differ from traditional management information system?

In decision support system (now maturing into business intelligent) user has the ability to construct a table (view, query) with any combination of the existing fields in all database.

The traditional MIS is confined to reports which although customize-able often become a one time design because of it's labour intensive nature.

As illustration, if traditional MIS is ordinary Excel table, decision support system is like the Excel pivot table.