Note7-Normalization0

Note7-Normalization0 - CSc 134 Database Management and File...

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1 CSc 134 Database Management and  File Organization 7. Functional Dependencies and  Normalization for Relational  Databases Ying Jin Computer Science Department California state University, Sacramento
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2 Introduction What is relational database design? The grouping of attributes to form relation schemas  What are good relational design? Formal measures
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3 Functional Dependencies FDs are  constraints  that are derived  from      meaning  and interrelationships   of the data  attributes A functional dependency is a property of  the  semantics  or  meaning of the  attributes .
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4 Definition of functional  dependency functional dependency , denoted by   Y, between two sets of attributes X  and Y that are subsets of R specifies a  constraint on the possible tuples that  can form a relation state r of R. The  constraint is that, for any two tuples t1  and t2 in r that have t1[X] = t2[x], they  must also have t1[Y]=t2[Y].
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5 FD example A set of attributes X  functionally  determines   a set of attributes Y if the  value of X determines a unique value  for Y. Social security number functionally  determines employee name SSN  ENAME
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6 Notation of Functional  Dependencies   Y function dependency from x to Y Y is functionally dependent on X X: left hand side FD. Y: right hand side FD Y holds if whenever two tuples have the  same value for X, they  must  have the same  value for Y A FD is a property of the relation schema R,  not of a particular legal relation state r of R. Y in R specifies a  constraint   on  all   relation instances r(R)
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7 Examples of FD Social security number determines employee  name SSN  ENAME Project number determines project name and  location PNUMBER  {PNAME, PLOCATION} Employee ssn and project number  determines the hours per week that the  employee works on the project {SSN, PNUMBER}  HOURS 
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8 Infer additional FDs Given a set of FDs F,  we can  infer   additional  FDs  that hold whenever the FDs in F hold. Given a set of functional dependencies F
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Note7-Normalization0 - CSc 134 Database Management and File...

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