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数据库系统 习题 答案

答案

一、 [12分] 用英文解释：

1. Query Language A query language in which a user requests information from the database.

2. First normal form (1NF) A relation schema R is in first normal form if the domain of all attributes of R are atomic.

3. View are virtual relations defined by a query language

二、 [10分] 填空题（在下列各小题中的括号部分省略了数据库系统的术语，在答

题纸上写好小题号，并在其后用英文填写相应的术语）：

1. An ( entity ) is an object that exists in the real world and is distinguishable from other objects.

2. The overall design of the database is called the (database schema ).

3. We say that a schedule S is ( conflict serializable ), if it is conflict equivalent to a serial schedule.

4. A ( relation ) is an association among several entities.

5. Let R be a relation schema. A subset K of R is a ( super key ) of R if, in any legal relation r(R), for all pairs t1 and t2 of tuples in r such that t1≠ t2, then t1[K]≠ t2[K].

6. Underlying the structure of a database is the ( Data model ): a collection of conceptual tools for describing data, data relationships, data semantics, and data constraints.

7. A (DML ) is a language that enables users to access or manipulate data.

8. A database schema is specified by a set of definitions that are expressed using a ( data dictionary).

9. A ( transaction ) is a unit of program execution that accesses and possibly updates various data items.

10. The ( lock-based protocol ) allows a transaction to lock a new data item only if that transaction has not yet unlocked any data item.

三、[12分] 设有属于1NF的关系模式R=（A, B, C, D, E），R上的函数依赖集 F ={AC DE, D B, AB C }

1、求属性集的闭包(AD).

2、R是否属于3NF ? 为什么?

3、R是否属于BCNF ? 为什么?

1．(AD)+=ADBCE

2．是

1 +

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