Define atom of domain relational calculus, Database Management System

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Define Atom of domain relational calculus

An atom has the outline < x1, x2, ... , xn > -> r , in which r stands for a relation on n attributes and x1, x2, ... , xn are the domain variables or domain constraints. 

 x Θ y , in which x and y are domain variables and Θ is the comparison operator (<, >,  <,  >, =, ≠).  It is needed that x and y have domains which can be compared by Θ. 

 x Θ c, in which x is a domain variable, Θ is a comparison operator, and c is a constraint in the domain of attributes for which x is a domain variable.


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