ex X -> Y # (left-hand side) -> (right-hand side)
when X -> Y holds, if Y is subset of X, then X -> Y is trivial FD
ex) X => { A, B, C }
subset of X => {}, { A }, { B }, { C }, { A, B }, {A, C}, {B, C}, { A, B, C }
{ A, B, C } -> {A, C} is trivial FD
{ A, B, C } -> {} is trivial FD
Y(right-hand side)가 X(right-hand side)의 subset일 때 trivial FD
when X -> Y holds, if Y is not subset of X, then X -> Y is Non-trivial FD
{ A, B, C } -> { B, C, D } is Non-trivial FD
{ A, B, C } -> { D, E } is Non-trivial FD & completely Non-trivial FD
when X -> Y holds, if any proper subset of X can determine Y, then X -> Y is partial FD
**proper subset**이란 X의 부분 집합이지만 X와 동일하지는 않은 집합
ex) X => { A, B, C }
subset => {}, { A }, { B }, { C }, { A, B }, {A, C}, {B, C}, { A, B, C }
proper subset => {}, { A }, { B }, { C }, { A, B }, {A, C}, {B, C}
when { empl_id, empl_name } -> { birth_date } holds, because { empl_id } can determine { birth_date } then this FD is Partial FD
when X -> Y holds, if every proper subset of X can not determine Y, then X -> Y is Full FD
when { stu_id, class_id } -> { grade } holds, because { stu_id }, { class_id }, { } can not determine { grade } then this FD is Full FD