對於任何一個圖G = (V;E) ，如果我們可以找到最少的k 個弦圖(V;Ei)，使得E = E1 \ \ Ek ，則我們定義此圖G = (V;E) 的chordality為k ；而一個圖G = (V;E) 的樹寬則被定義為此圖所有的樹分解的寬的最小值。在這篇論文中，最主要的結論是所有圖的chordality 會小於或等於它的樹寬；更特別的是，有一些平面圖的chordality 為3，而所有系列平行圖的chordality 頂多為2。 / The chordality of a graph G = (V;E) is dened as the minimum k such that we can write E = E1 \ \ Ek, where each (V;Ei) is a chordal graph. The treewidth of a graph G = (V;E) is dened to be the minimum width over all tree decompositions of G. In this thesis, the principal result is that the chordality of a graph is at most its treewidth. In particular, there are planar graphs with chordality 3, and series-parallel graphs have chordality at most 2.