
Example of a Range Relation expression:
Employee(t) 

{ t  CONDITION(t) } Meaning: Retrieve all tuples t for which the condition CONDITION(t) is true 
{ t  Employee(t) AND t.salary > 40000 } Meaning: Retrieve all tuples t such that: Employee(t) is true (t is a tuple from Employee) and t.salary > 40000 is true Rephrased: t is a tuple of the relation Employee and t.salary > 40000 
Concrete example:

{ t.fname, t.lname  Employee(t) AND t.salary > 50000 } Meaning: Retrieve fname and lname of employees whose salary > 50000 
{ t.salary  Employee(t) AND t.fname='John' AND t.lname='Smith' } Meaning: Retrieve the salary of the employee "John Smith" 