1. Name three sources for databases.

   (1) 现存数据
   (2) 新信息系统的发展
   (3) 现存数据库的重新设计
   

2. Describe the characteristics of a table that make it a relation. Define the term domain and explain the significance of the domain integrity constraint to a relation.

   域：描述数据表中某一属性的取值类型和范围
   （1）域完整性是针对某一具体关系数据库的约束条件，它保证表中某些列不能输入无效的值
   （2）域完整性指列的值域的完整性。如数据类型、格式、值域范围、是否允许空值等
   （3）域完整性限制了某些属性中出现的值，把属性限制在一个有限的集合中
   

3. Give an example of two tables that are not relations.

   The table in Figure 3-7 is not a relation, because the entries for employees Caruthers and Caldera require a particular row arrangement. If the rows in this table were rearranged, we would not know which employee has the indicated Fax and Home numbers.
   

4. Suppose that two columns in two different tables have the same column name. What convention is used to give each a unique name?

   假设两张不同的表为T1和T2，相同的列为number，我们可以分别命名为T1.number和T2.number.
   

5. Must all the values in the same column of a relation have the same length?

   即使一个关系的每一个单元格必须有一个单一的值，这并不意味着所有的值必须有相同的长度
   

6. Explain the three different sets of terms used to describe tables, columns, and rows.

   由Codd的定义，大多数从业者表指的是关系，关系中的列称为属性，和关系中的行称为元组
   

7. Explain the difference between functional dependencies that arise from equations and those that do not.

   从公式中产生的函数依赖可以让我们计算出确定的值，而不是从公式中产生的函数依赖可以让我们知道不同关系的特征
   

8. Explain the intuitive meaning of the functional dependency.
   PartNumber→PartWeight

   PartNumber决定PartWeight
   

9. Explain the following statement: “The only reason for having relations is to store instances of functional dependencies.”

   假设我们有一个表ObjectColor → (Weight, Shape),我们可以通过ObjectColor公式计算Weight和Shape，那么我们就不需要这个表
   

10. Explain the meaning of the expression:
    (FirstName, LastName) → Phone

    FirstName和LastName共同决定Phone
    

11. What is a composite determinant?

    两列或两列以上的决定因素
    

12. If (A, B) →C , then can we also say that A→C?

```
不可以
```

13. If A→ (B, C), then can we also say that A→ B?

    可以
    

14. If it is true that
    PartNumber →PartWeight
    does that mean that PartNumber will be unique in a relation?

    不是，可能还有别的因素决定PartWeight
    

15. Under what conditions will a determinant be unique in a relation?

    这个决定因素可以决定其他所有列
    

16. What is the best test for determining whether a determinant is unique?

    最好的策略是考虑产生数据的业务活动的性质，并询问用户
    

17. What is a composite key?

    拥有两列或两列以上的码
    

18. What is a candidate key?

    在一个关系中可以决定其他所有列的码
    

19. What is a primary key? Explain the significance of the entity integrity constraint to a primary key.

    在设计数据库时，选择一个候选码作为主码；实体完整性约束规定主码不能为空值
    ```
    
20. Explain the difference between a candidate key and a primary key.

    ```
    一张表可以有多组候选码但是只能有一组主码
    ```

21. What is a surrogate key?

    ```
    代理码是人工添加到表中用作主键的列
    ```

22. Where does the value of a surrogate key come from?

    ```
    在创建行时，DBMS为代理码指定一个唯一且不变的值
    ```

23. When would you use a surrogate key?

    ```
    当主码冗余且复杂时
    ```

24. What is a foreign key? Explain the significance of the *referential integrity constraint* to a
     foreign primary key.

    ```
    外码是在本表中不作为码而在另外一组关系表中作为主码的码；
    参照完整性约束规定外码必须存在于其作为主码的表中或为空值。

25. What is a normal form?

    范式是符合某一种级别的关系模式的集合
    

26. Explain why duplicated data lead to data integrity problems.

    任何具有重复数据的表都容易发生更新异常
    

27. What relations are in 1NF?

    数据库的每一列都是不可分割的数据项
    

28. Which normal forms are concerned with functional dependencies?

    BCNF, 3NF and 2NF
    

29. What conditions are required for a relation to be in 2NF?

    满足第一范式，且每一个非主属性完全函数依赖任何一个候选码
    

30. What conditions are required for a relation to be in 3NF?

    满足第二范式，且数据库表中不包含已在其它表中已包含的非主关键字信息
    

31. What conditions are required for a relation to be in BCNF?

    所有非主属性对每一个码都是完全函数依赖；
    所有主属性对每一个不含它的码也是完全函数依赖；
    没有任何属性完全函数依赖于非码的任何一组属性。
    

32. If a relation is in BCNF, what can we say about it with regard to 2NF and 3NF?

    能，它既是第二范式也是第三范式
    

33. What normal form is concerned with multivalued dependencies?

    4NF
    

34. Summarize the three categories of normalization theory.

    第一个涉及函数依赖引发的异常；
    第二个涉及多值依赖引发的异常；
    第三个涉及数据约束和特殊条件引发的异常。
    

35. In general, how can you transform a relation not in BCNF into ones that are in BCNF?

```
重新设计表使所有决定因素都是候选码
```

36. What is a referential integrity constraint? Define the term, and give an example of its use. Are null values allowed in foreign key columns with a referential integrity constrain? How does the referential integrity constrain contribute to database integrity?

    参照完整性约束是对关系数据库中建立关联关系的数据表间数据参照引用的约束，也就是对外码的约束；
    具有参照完整性约束的外码列中可以使用空值；
    参照完整性约束可以维护表间数据的有效性。
    

37. Explain the role of referential integrity constraints in normalization.

    以确保数据库中存储的数据正确、有效、相容。
    

38. If a determinant is part of a candidate key, is that good enough for BCNF?

    不符合BC范式
    

39. How does a multivalued dependency differ from a functional dependency?

    在关系数据库理论中，函数依赖是关系中来自数据库的两组属性之间的约束；多值依赖是关系中两组属性之间的完全约束。
    

40. Consider the relation:
    PERSON (Name, Sibling, ShoeSize)

    Assume that the following functional dependencies exist:
    Name→→ Sibling
    Name → ShoeSize
    Describe deletion, modification, and insertion anomalies for this relation.

    具体列进行删除修改和插入后分析
    

41. Place the PERSON relation in Review Question 40 into 4NF.

    (Name, Sibling),(Name, ShoeSize)
    

42. Consider the relation:
    PERSON_2 (Name, Sibling, ShoeSize, Hobby)
    Assume that the following functional dependencies exist:
    Name →→ Sibling
    Name → ShoeSize
    Name →→ Hobby
    Describe deletion, modification, and insertion anomalies for this relation.

    具体列进行删除修改和插入后分析
    

43. Place the PERSON_2 relation in Review Question 42 into 4NF.

    (Name, Sibling),(Name, ShoeSize),(Name, Hobby)