Predicate Calculus Formula Set of attributes and constants Set of comparison operators:(e.g,<,≤，=，≠，>，≥) ■ Set of connectives:and (A),or (v),not ( ■Implication(→)：x→y,if x if true,then y is true X→y=XVy Set of quantifiers: ·3t∈r(Q(t)="there exists”a tuple in t in relation r such that predicate Q(t)is true 。tt∈r(Q(t)）=Q is true“for all"tuples t in relation r Database System Concepts-7th Edition 27.5 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 27.5 ©Silberschatz, Korth and Sudarshan th Edition Predicate Calculus Formula ▪ Set of attributes and constants ▪ Set of comparison operators: (e.g., , , =, , , ) ▪ Set of connectives: and (), or (v)‚ not () ▪ Implication (): x  y, if x if true, then y is true x  y  x v y ▪ Set of quantifiers: •  t  r (Q (t ))  ”there exists” a tuple in t in relation r such that predicate Q (t ) is true • t  r (Q (t ))  Q is true “for all” tuples t in relation r