Data Base Size Is Decreased on sap Business one

Hi

Every day i monitoring Data base But Today i Observed DB Size is Decreased ,But  it's  not Happened last One year Onwards..The Difference Size Morning to Evening all most 630MB , what was the Problem But last year june and August also happened same Problem But not this much size ,That Time  300 MB only  ..

  What was the Problem??

just now i noticed above the   problem..

Thanks&Regards

AndakondaRamudu