Choice of Decompositions

• There are 2 ways to decompose CSJDPQV into BCNF:

  • SDP and CSJDQV; lossless-join but not dep-preserving.
  • SDP, CSJDQV and CJP; dep-preserving as well.

• The difference between these is really the cost of enforcing the FD JP ? C.

  • 2nd decomposition: Index on JP on relation CJP.
  • 1st:

CREATE ASSERTION CheckDep

CHECK ( NOT EXISTS ( SELECT *

FROM PartInfo P, ContractInfo C

WHERE P.sid=C.sid AND P.did=C.did

GROUP BY C.jid, P.pid

HAVING COUNT (C.cid) > 1 ))

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