Category (strong entity) - Category ID (single value, simple numeric), pk - Category Name (single value, simple string) Isa_Category (Category Has Category) Roles: Category fulfills the subclass role and Supercategory fulfills the superclass role. Cardinality: n:1, a super category can have many subcategories Participation: Supercategory is total, there must be a supercatory for each subcategory, but supcategory is partial, not every supercategory must have a subcategory to exist.怎样转化为关系模型

可以将上述实体及其关系转化为以下关系模式：

Category(CategoryID, CategoryName)
- CategoryID: 单值、简单数值，作为主键
- CategoryName: 单值、简单字符串，表示类别名称

Isa_Category(SubcategoryID, SuperCategoryID)
- SubcategoryID: 表示子类别ID，参照Category表的CategoryID字段
- SuperCategoryID: 表示父类别ID，参照Category表的CategoryID字段

其中，Category表表示类别实体，Isa_Category表示类别间的继承关系。在Isa_Category表中，SubcategoryID和SuperCategoryID均参照Category表的CategoryID字段，表示子类别和父类别的关系。在Isa_Category表中，一个父类别可以对应多个子类别，但一个子类别只能有一个父类别。同时，Category表中的CategoryID字段作为主键，保证了每个类别在实体层面的唯一性。

相关问题

使用映射算法将 ER 架构映射到关系数据库架构。使用以下表示法表示生成的关系数据库架构：PK 表示主键，AK 表示备用键，FK 表示外键，并带有指向相应表（主键）的箭头 Book Entity (Strong) - Title (single valued, simple string) - ISBN (single valued, simple alphanumeric string), pk - Edition (single valued, simple numeric) - Date of Publication (single valued, composite concatenation of characters and numbers) - Price (single valued, simple floating point number) - Book Description (single valued, simple string) Author Entity (Strong) - Author Name - Author_id, pk Publisher Entity (Strong) - Publisher id (single value, simple numeric), pk - Publisher Name (single valued, simple string) - Address (single valued, simple string) - together the publisher name and address could make an alternate key because no to publishers can have the same name and address Customer Entity (strong) - Customer_id (single valued, simple string), pk - Name (composite one value for first, middle and last name, simple string) - Mailing Address (single valued, simple string) - Credit Card Number and Expiration Date (single value, simple numeric sequence), alternate key - Phone Number (single value, simple alphanumeric string) - Email Address (single valued, simple alphanumeric string) Shipment (strong) - Date of Shipment ( single valued, composite of strings and numbers) - Tracking Number (single valued, simple alphanumeric string), pk - Date of Expected Delivery ( single valued, compoite of strings and numbers) Order (Strong) - Order Number (single valued, simple number), pk - Mailing Address (single value, simple string) - Method of Shipment (single value, simple string) - Date and Time of Order (when the order was placed) - Total Price of the Order (multivalue, composite) Promotion (strong entity type ) - Promotion id number, pk - Percentage Discount Points (single value, simple float) - Duration of Promotion (start date and end date) ( composite attributes like the dates above) Line Item(weak entity type) - Total price for each book that is ordered (single value, two place precision float) - Quantity of each item ordered Category (strong entity) - Category ID (single value, simple numeric), pk - Category Name (single value, simple string)，

将ER架构映射到关系数据库架构，生成的关系数据库架构如下：

Book 表：
- ISBN (主键)
- Title
- Edition
- Date of Publication
- Price
- Book Description

Author 表：
- Author_id (主键)
- Author Name

Publisher 表：
- Publisher id (主键)
- Publisher Name
- Address
- AK: Publisher Name + Address

Customer 表：
- Customer_id (主键)
- Name
- Mailing Address
- Phone Number
- Email Address
- AK: Credit Card Number and Expiration Date

Shipment 表：
- Tracking Number (主键)
- Date of Shipment
- Date of Expected Delivery

Order 表：
- Order Number (主键)
- Mailing Address
- Method of Shipment
- Date and Time of Order
- Total Price of the Order

Promotion 表：
- Promotion id number (主键)
- Percentage Discount Points
- Duration of Promotion (start date and end date)

Line Item 表：
- Book ISBN (外键指向 Book 表)
- Order Number (外键指向 Order 表)
- Total price for each book that is ordered
- Quantity of each item ordered

Category 表：
- Category ID (主键)
- Category Name

需要注意的是，Line Item 表是一个弱实体类型，需要使用两个外键来指向 Book 表和 Order 表。另外，Promotion 表中的 Duration of Promotion 属性是一个复合属性，可以拆分成两个单独的属性来存储。