Let $k$ be an algebraically closed field with $\operatorname{char}(k) = 0$. The assignment sending a finite-dimensional semisimple Lie algebra $\mathfrak{g}$ over $k$ to the finite disjoint union of the Dynkin diagrams of the irreducible components of its root system induces a bijection between isomorphism classes of finite-dimensional semisimple Lie algebras over $k$ and finite disjoint unions of Dynkin diagrams of types $A_n$ for $n \geq 1$, $B_n$ for $n \geq 2$, $C_n$ for $n \geq 3$, $D_n$ for $n \geq 4$, $E_6$, $E_7$, $E_8$, $F_4$, and $G_2$.

Under this bijection, direct sums of semisimple Lie algebras correspond to disjoint unions of Dynkin diagrams.