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442_Review_Relational

442_Review_Relational - Review:TheRelationalModel 198:442...

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Review: The Relational Model 198:442 Rutgers University
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Relational Database: Definitions Relational database :   a set of  relations Relation:  made up of 2 parts: Instance  : a  table ,  with rows and columns.  #Rows =  cardinality , #fields =  degree / arity. Schema  :   specifies   name of relation, plus name and type of  each column. E.G. Students( sid : string,  name : string,  login : string,  age : integer,  gpa : real). Can think of a relation as a  set   of rows or  tuples  (i.e.,  all rows are distinct).
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Example Instance of Students Relation Rutgers University sid  name  login  age  gpa  53666  Jones  [email protected]  18  3.4  53688  Smith  [email protected]  18  3.2  53650  Smith  [email protected]  19  3.8   Cardinality = 3, degree = 5, all rows distinct  Do all columns in a relation instance have to     be distinct?
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Integrity Constraints (ICs) IC:  condition that must be true for  any 
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