lossless decomposition

Question

I know the condition for a 2 table to be lossless, but i cannot visualize it.

How is 1 table which is decomposed, and if common attribute is key in any one of table, then its lossless decomposition.

Can anyone explain me this with different analogy or help me visualize it.

Answer 1

Check these links

http://www.edugrabs.com/lossy-join-decomposition/

Why Lossy Join Decomposition is called Lossy although the relation is getting extra tuples ? 

    ⇒ Because we are loosing original Data.

https://gateoverflow.in/91049/lossy-join-decomposition

https://stackoverflow.com/questions/12671362/lossy-decomposition

Answer 2

R(A,B,C,D)

if decomposed into two relations :-

R1(A,B,C) R2(B,D)

AB->C

B->D

If(R1 intersection R2 = Some key) then decomposition is lossless else lossy

 SO R1 intersection R2 = B which is a key and define all attributes of R2 then Lossless