By using decomposition rules, all functional dependencies become functional dependencies with only one attribute on the right. From the title, the right half of any function in F contains only one attribute: {A→B, B→A, B→C, A→C, C→A}

In the second step, if the order of redundancy removal is different, the results will be different, so there is more than one minimum functional dependency set, and another minimum functional dependency set can be found: {A→B, B→A, A→C, C→A}

Given a number set A, assuming that the element in it is X, now apply the corresponding rule F to the element X in A, and record it as f(x), and get another number set B. Assuming that the element in B is Y, the equivalent relationship between Y and X can be expressed as y=f(x). The concept of function includes three elements: definition field A, value field C and corresponding rule F, among which the core is corresponding rule F, which is the essential feature of function relationship.

Extended data:

The corresponding rules of functions are usually expressed by analytical expressions, but a large number of functional relationships can not be expressed by analytical expressions, but only by images, tables and other forms.

Functions are related to inequalities and equations (elementary functions). Let the function value be equal to zero. From a geometric point of view, the value of the corresponding independent variable is the abscissa of the intersection of the image and the X axis. From the algebraic point of view, the corresponding independent variable is the solution of the equation.

In addition, replacing "=" in the expression of a function (except a function without expression) with "",and then replacing "y" with other algebraic expressions, the function becomes an inequality, and the value range of the independent variable can be found.

Baidu Encyclopedia-Function