Contains references to the attributes used to identify an instance of the entity to the user 包含对用来为用户标识实体实例的属性的引用。
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The mapping rule from express data schema to relational databases schema is studied . the translation of the different semantic data types of express into the data definition language of sql is discussed . the persistency of step data in relational databases is realized based on an entity instance manager in working form 论文对express信息模型到关系数据库模型的映射规则进行了研究，详细分析了express语言的不同数据类型到sql数据类型的转化方法，并对内存实现方式的产品数据仓库的结构、功能进行了研究，阐述了基于关系数据库的实体实例索引表的建立方法。
