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PowerDesigner的概念数据模型CDM

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Jun 07, 2016 pm 05:05 PM

powerdesigner

概念数据模型（Conceptual Data Model）也称信息模型，以实体-关系理论作为基础，并对其进行扩充；从用户的视角出发对信息数据进

概念数据模型（Conceptual Data Model）也称信息模型，以实体-关系理论作为基础，并对其进行扩充；从用户的视角出发对信息数据进行建模，主要用于数据库的概念设计，人们将现实世界抽象为概念世界，然后在讲概念化的数据转换为计算机可以理解的模型；

CDM是一组严格定义的模型元素的集合，这些模型元素精确的描述了系统的静态特性、动态特性以及完整性约束条件等等，其中包含了数据结构、数据操作和完整性约束三部分；

数据模型的一般性特征：

1、现实世界中数据特征的抽象；

2、比较真实的模拟了现实世界；

3、容易被人理解；

4、可以转换，用计算机实现；

绘制顾客购买商品时的CDM图》

新建CDM

新建实体

属性设置

特征识别

主（次）标识符属性勾选（界定每个实体的不同标识）

制作可附加在实体上作为实体的属性的数据项（信息存储的最小单位）

设置数据项的唯一性代码选项和重用选项：Unique code》每个数据项在同个命名空间有唯一的代码；Allow Reuse》一个数据项可以充当多个实体的属性；

绘制一个实体成功

多个实体间的关系，，连线开叉一端代表多，不开叉一端代表一，小圆圈一端代表可选，小十字一端代表强制；

多个实体绘制成功

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