【摘要】 任何复杂的聚合实体都是由属性和满足3NF的简单实体聚合而成的。本文通过对大量实体的研究,总结出聚合实体的四种基本类型,即特征聚合、联合聚合、合成聚合和复杂聚合。每种聚合类型对应一种数据结构图和ER模型。把系统中各个聚合实体所对应的ER模型汇总到一起就得到系统的ER模型。更多还原

【Abstract】 All complex aggregation entities are composed of attributes and simple entities that Satisfy 3NF.The paper sumes up characteristic, association integration, and composition aggregation types in studying many aggregation entities. Every aggregation type corresponds to a data structure diagram and an entity relationship model. Collectting different ER models of aggregation entities may derive total ER model in a system.更多还原