数据库设计：解释这个模式(Database Design: Explain this schema)

 充分披露...在这里试着狂热地学习更多关于数据库的知识，所以我正在努力，并试图从源头获得这个答案，但无济于事。 
 
 来自databaseanswers的Barry Williams已经发布了这个模式。 
 
 客户和费用模式 
 
 
 我试图了解此架构中地址表的拆分。 我清楚地知道Addresses表包含给定地址的细节。 Client_Addresses和Staff_Addresses表是我的最佳选择。 
 
 1）我理解如所示的主外键的使用，但我假设当使用这些外键时，在同一个表中没有常驻主键（在这种情况下为date_address_from）。 有人可以解释两者的推理，并说出这实际上是如何工作的吗？ 
 
 2）为什么你会使用date_address_from作为主键而不是像client_address_id那样的PK？ 如果某人在一天之内输入两个地址，他的设计会有冲突吗？ 如果是，如果不是，那是什么？ 
 
 3）沿着规范化的路线......因为date_address_from和date_address_to在Client_Addresses和Staff_Addresses表中都应该相同，所以这些字段只是不包含在主地址表中？ 

Full disclosure...Trying feverishly here to learn more about databases so I am putting in the time and also tried to get this answer from the source to no avail.
 
Barry Williams from databaseanswers has this schema posted. 
 
Clients and Fees Schema
 
 
I am trying to understand the split of address tables in this schema. Its clear to me that the Addresses table contains the details of a given address. The Client_Addresses and Staff_Addresses tables are what gets me. 
 
1) I understand the use of Primary Foreign Keys as shown but I was under the assumption that when these are used you don't have a resident Primary Key in that same table (date_address_from in this case). Can someone explain the reasoning for both and put it into words how this actually works out?
 
2) Why would you use date_address_from as the primary key instead of something like client_address_id as the PK? What if someone enters two addresses in one day would there be conflicts in his design? If so or if not, what?
 
3) Along the lines of normalization...Since both date_address_from and date_address_to are the same in the Client_Addresses and Staff_Addresses table should those fields just not be included in the main Address table?

原文：https://stackoverflow.com/questions/4663366