The arrow notation here is not material implication, but function evaluation. The function itself can be interpreted as an Indicator Function[1] for the employe

The arrow notation here is not material implication, but function evaluation. The function itself can be interpreted as an Indicator Function[1] for the employee set, or alternatively, as simply evaluating the predicate. In terms of tables, the rows are exactly the subset of predicates that are TRUE. So FALSE statements like the second one are indicated by their absence in the employee table. [1] http://en.wikipedia.org/wiki/Indicator_function http://en.wikipedia.org/wiki/Indicator_function