在考虑平面上“点类”和“矩形类”的关系时，由于出发点不同，可以有多种方式，例如：可以认为一个矩形对象由两个点类对象组成（左上角和右下角），也可以认为矩形是在点的基础上加上宽和高构成的，-considering the plane "in category" and "rectangle" in the relationship, as the starting point will be different, a variety of forms, such as : a rectangle that can be targeted by the two types of objects composed points (upper left and lower right), could also be considered in rectangular points on the basis of added width and high consisting of,