Choice of Decompositions (Contd.)

• The following ICs were given to hold: JP ? C, SD ? P, C is the primary key.

• Suppose that, in addition, a given supplier always charges the same price for a given part: SPQ ? V.

• If we decide that we want to decompose CSJDPQV into BCNF, we now have a third choice:

  • Begin by decomposing it into SPQV and CSJDPQ.
  • Then, decompose CSJDPQ (not in 3NF) into SDP, CSJDQ.
  • This gives us the lossless-join decomp: SPQV, SDP, CSJDQ.
  • To preserve JP ? C, we can add CJP, as before.

• Choice: { SPQV, SDP, CSJDQ } or { SDP, CSJDQV } ?

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