Abstract: The semantic concept of the program is the syntax and accidence of the abstract expressed，but semantic concept in the software constituted the human thought hands over with machine thought with each other the middle transformation of the process. This paper present the meaning of semantic equivalence and Herbrand equivalence based upon denotational sematics with concrete programming language.Herbrand equivalence is weaker than Semantic equivalence, it has much wider utility. Several applications of simple algorithms were presented, through which we see clearly the advantages and limitations of Herbrand equivalence .

Key words: Program Understanding, Algorithm Recognition, Semantic Equivalence, Term Computed, Herbrand Equivalence

摘要： 蕴涵在程序代码中的语义是程序语言词法和语法的抽象表达，构成了人脑思维与机器思维交互过程的中间变换。从指称语义出发，结合具体语言，用形式化的方法讨论了语义等价和H-等价（Herbrand等价）。H-等价的判定条件相对来说更容易得到满足，具有更广泛的可用性。结合具体算法给出了H-等价在算法识别方面的应用成果及其局限性。

关键词: 程序理解, 算法识别, 语义等价, 计算项, H－等价