The document discusses the relational model for databases. The relational model represents data as mathematical n-ary relations and uses relational algebra or relational calculus to perform operations. Relational calculus comes in two flavors: tuple relational calculus (TRC) and domain relational calculus (DRC). TRC uses tuple variables while DRC uses domain element variables. Expressions in relational calculus are called formulas and queries return tuples that make the formula evaluate to true.
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