函数依赖集闭包计算示例 - {AB→C, B→D, AC→D, CD→A}

首先，将给定的函数依赖集转化为关系模式： R = {ABC, BD, ACD, CDA}

然后，找出所有可能的函数依赖集，包括R本身和所有可能的子集： {A}+ = {A} {B}+ = {BD} {C}+ = {CDA} {D}+ = {D}

{AB}+ = {ABCD} {AC}+ = {ACD} {AD}+ = {ABCD} {BC}+ = {BCD} {BD}+ = {BD} {CD}+ = {CDA}

{ABC}+ = {ABCDA} {ABD}+ = {ABCD} {ACD}+ = {ACD} {BCD}+ = {BCDA} {CDA}+ = {CDA}

{ABCD}+ = {ABCD}

因此，函数依赖集的闭包为： {A}+, {B}+, {C}+, {D}+, {AB}+, {AC}+, {AD}+, {BC}+, {BD}+, {CD}+, {ABC}+, {ABD}+, {ACD}+, {BCD}+, {CDA}+, {ABCD}+