关键词: 实体-联系（E-R）模型, 键无效, 联系状态, 动态联系, 转换规则

Abstract: The translating of Entity-Relationship model into Relational Data model is an important process of a database design. There are some defects in the traditional rules of translating, and these errors usually lead to a problem（called invalid-key） in a relation schema coming from the Translating. This paper provides an exhaustive analysis of the problem, and shows that time-varying of relationship is the main reason which causes an invalid-key problem. This paper develops a new property for relationship, called state, and divides relationship into dynamic and static. This paper presents new rules of translating. It eliminates the defects in traditional rules, and solves the invalid-key problem.

Key words: Entity-Relationship, invalid-key, state of relationship, dynamic relationship, rule of translating