viewnotes/247/Database Management System 10CS54 VTU unit 6

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Which Normal form is based on a concept of MVD?Database Management Systems - 10CS54 VTU notes (Jan 2013/July 2013/Jan 2014)

explain the same with example? 


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Multivalued Dependencies and Fourth Normal Form (4NF) 4NF associated with a dependency called multi-valued dependency (MVD). MVDs in a relation are due to first normal form (1NF), which disallows an attribute in a row from having a set of values. MVD represents a dependency between attributes (for example, A, B, and C) in a relation, such that for each value of A there is a set of values for B, and a set of values for C. However, the set of values for B and C are independent of each other. MVD between attributes A, B, and C in a relation using the following notation  A - > - > B (A multidetermines B) A - > - > C 

A multivalued dependency (MVD) X Y specified on R, where X, and Y are both subsets of R and Z = (R – (X Y)) specifies the following restrictions on r(R) t3[X]=t4[X]=t1[X]=t2[X] t3[Y] = t1[Y] and t4[Y] = t2[Y] t3[Z] = t2[Z] and t4[Z] = t1 [Z] 
Fourth Normal Form (4NF) A relation that is in Boyce-Codd Normal Form and contains no MVDs. BCNF to 4NF involves the removal of the MVD from the relation by placing the attribute(s) in a new relation along with a copy of the determinant(s). A Relation is in 4NF if it is in 3NF and there is no multivalued dependencies. 


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