简体繁体 English

建模或关系？

[英]modeling OR relationships?

原文 2010-11-12 18:03:37 9 3 database/ normalization/ entity-relationship/ relationships

How do you trasnlate OR relationships in ER diagrams? 您如何在ER图中转换OR关系？ For example, you have 2 entities that have some connection with the third, but only one of them can have that relation?(ex. BussinessOwner or PrivateOwner can hold just one Property ) ? 例如，您有2个实体与第三个实体有某种联系，但是只有其中一个实体可以具有这种关系？（例如， BussinessOwner或PrivateOwner只能拥有一个Property ）？

3 个解决方案

Option 1 (easier): Two nullable foreign keys, BusinessOwnerID and PrivateOwnerID. 选项1（更轻松）：两个可为空的外键，BusinessOwnerID和PrivateOwnerID。

Option 2 (more normalized): Both BusinessOwner and PrivateOwner are Owners, so you could make an Owner entity with whatever information is common between BusinessOwner and PrivateOwner. 选项2（更规范化）：BusinessOwner和PrivateOwner都是所有者，因此您可以使用在BusinessOwner和PrivateOwner之间共有的任何信息来创建Owner实体。 Then add an OwnerID to both the BusinessOwner and PrivateOwner tables. 然后将OwnerID添加到BusinessOwner和PrivateOwner表中。

Like this: 像这样：

http://consultingblogs.emc.com/davidportas/archive/2007/01/08/Distributed-Keys-and-Disjoint-Subtypes.aspx http://consultingblogs.emc.com/davidportas/archive/2007/01/08/Distributed-Keys-and-Disjoint-Subtypes.aspx

User an owner and Type Field. 用户owner和Type字段。 Not 2 owner Fields. 不是2个所有者字段。

Owners are People entity. 所有者是人实体。 Types are Type entity or strings ("Business" Owner or "Private Owner") 类型是类型实体或字符串（“业务”所有者或“私人所有者”）

What if you add a new type... "Sr. Partner" With your model you would have to add new filed and recode your business rules. 如果添加新类型，该怎么办...“高级合作伙伴”对于您的模型，您将必须添加新的字段并重新编码您的业务规则。