线性表：数据间关系是线性的，每个元素只有一个前趋，一个后续，1：1；

树：有着明显的层次关系，每个元素只有一个前趋，但有多个后续，1：N；

图：数据之间的关系是任意，每个元素的前趋和后续个数是不定的，M：N；

-Linear form: the relationship between the data is linear, each element has only one predecessor, a follow-up, 1:1　tree: there is a clear hierarchy, each element has only one predecessor, but there are several follow-up, 1 : N　Figure: the relationship between the data is arbitrary, the precursor of each element and follow-up number is uncertain, M: N