title: lossy decomposition
body: <p>Why a lossy decomposition is called lossy ? What exactly we loss in a lossy decomposition?</p>
  
  <p>There is a relation R. It is decomposed into two relation R1 and R2.</p>
  
  <p>if  R = (R1 JOIN R2)  then it is losless join decomposition.It is alright.</p>
  
  <p>if R is a subset of (R1 JOIN R2) then lossy join decomposition.</p>
  
  <p>Here is lossy join decomposition, after join R1 and R2 we are actually getting more records compare to R. So what are we losing. ?</p>