8/8/2019 Chun ha d liu trong CSDL quan h

1/1

Chun ha d liu trong CSDL quan h

Cc khi nim v CSDL quan h cc bn ghi trn lp, di y ch l cc kin thcchnh, khng nh ngha li .

Mch ch ca chun ha d liu trong CSDL quan h :+ Trnh tnh trng tha, lng ph nh, phc tp CSDL+ Gim thiu vic s dng cc gi tr rng+ Ngn nga mt thng tin khi update CSDL (Delete, Create, Move, ..)

Cc dng chun ha d liu c bn :+ 1NF (first normal form - dng chun 1) : khng cha cc thc tnh a tr, hay cc ca bng khng cha nhiu hn 1 gi tr+ 2NF (second normal form - dng chun 2) : l dng chun 1 v cc thc tnh khng phi kha th n phi ph thc hon ton vo kha chnh+3NF (third normal form - dng chun 3) : l dng chun 2 v khng c s ph thc hm

bc cu.+ Boyce-codd : (BCNF) (c thm gio trnh )