《数据库管理系统原理与设计答案第三版中英对照》【推荐】20个字

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Database Management Systems Principles and Design Solutions Manual (Third Edition) is a comprehensive guide written by Raghu Ramakrishnan and Johannes Gehrke, alongside Jeff Derstadt, Scott Selikoff, and Lin Zhu. This manual serves as a valuable resource for students and professionals alike who are looking to deepen their understanding of database management systems. In this third edition, the authors delve into the fundamental principles and concepts of database systems, starting with an introduction to database systems and design. The relational model is explored in depth, covering topics such as relational algebra, relational calculus, SQL, and relational database design. One of the key highlights of this manual is the detailed answers provided to all the questions and exercises at the end of each chapter. These solutions offer valuable insights and explanations to help readers grasp the core concepts and master the practical applications of database management. With a focus on practical examples and real-world scenarios, this manual equips readers with the knowledge and skills needed to design, implement, and manage databases effectively. Whether you are a student studying database systems or a professional working in the field, this manual is an invaluable tool for enhancing your expertise and understanding in this important area of computer science. Overall, Database Management Systems Principles and Design Solutions Manual (Third Edition) is a comprehensive and authoritative guide that covers all aspects of database management systems. The combination of theoretical foundations and practical applications makes it a must-have resource for anyone looking to excel in the field of database management.

2 Chapter 1

2 第一章

Concurrent access and crash recovery. A DBMS supports the notion of a trans-action,

which is conceptually a single user’s sequential program. Users can write transactions

as if their programs were running in isolation against the database. The DBMS executes

the actions of transactions in an interleaved fashion to obtain good performance, but

schedules them in such a way as to ensure that conflicting operations are not permitted

to proceed concurrently. Further, the DBMS main-tains a continuous log of the changes

to the data, and if there is a system crash, it can restore the database to a transaction-

consistent state. That is, the actions of incomplete transactions are undone, so that the

database state reflects only the actions of completed transactions. Thus, if each

complete transaction, executing alone, maintains the consistency criteria, then the

database state after recovery from a crash is consistent.

并发访问和崩溃恢复。数据库管理系统支持事务处理的概念，从概念上讲，事务

处理是单个用户的顺序程序。用户可以写事务，就好像他们的程序是独立运行在

数据库上一样。

DBMS

以交错的方式执行事务操作以获得良好的性能，但是以确

保不允许并发执行冲突操作的方式安排这些操作。此外，

DBMS

主要维护数据更

改的连续日志，如果发生系统崩溃，它可以将数据库恢复到事务一致的状态。也

就是说，不完整事务的操作被撤消，因此数据库状态只反映已完成事务的操作。

因此，如果每个完整的事务，单独执行，保持一致性标准，那么从崩溃中恢复后

的数据库状态是一致的。

If these advantages are not important for the application at hand, using a collection of files

may be a better solution because of the increased cost and overhead of purchasing and

maintaining a DBMS.

如果这些优势对于手头的应用程序并不重要，那么使用一组文件可能是一个更好的解

决方案，因为购买和维护 DBMS 的成本和开销增加了。

Exercise 1.2 What is logical data independence and why is it important?

练习 1.2 什么是逻辑数据独立性，为什么它很重要？

Answer 1.2 Logical data independence means that users are shielded from changes in the

logical structure of the data, i.e., changes in the choice of relations to be stored. For example,

if a relation Students(sid, sname, gpa) is replaced by Studentnames(sid, sname) and

Studentgpas(sid, gpa) for some reason, application programs that operate on the Students

relation can be shielded from this change by defining a view Stu-dents(sid, sname, gpa) (as

the natural join of Studentnames and Studentgpas). Thus, application programs that refer to

Students need not be changed when the relation Stu-dents is replaced by the other two

relations. The only change is that instead of storing Students tuples, these tuples are

computed as needed by using the view definition; this is transparent to the application

program.

答案 1.2 逻辑数据独立性意味着用户不会受到数据逻辑结构变化的影响，即存储关系

选择的变化。例如，如果一个关系 Students (sid ， sname ， gpa) 由于某种原因被

Studentnames (sid，sname)和 studentgpa (sid，gpa)替换，那么可以通过定义一个视图

stu-Students (sid，sname，gpa)(作为 Studentnames 和 studentgpa 的自然连接)来屏蔽在

Students 关系上运行的应用程序。因此，当关系 stu-Students 被另外两个关系替换时，

引用 Students 的应用程序不需要更改。唯一的变化是，不存储 Students 元组，而是使

用视图定义根据需要计算这些元组; 这对应用程序是透明的。

Exercise 1.3 Explain the di erence between logical and physical data independence.ﬀ

练习 1.3 解释逻辑数据独立性和物理数据独立性的区别。

Answer 1.3 Logical data independence means that users are shielded from changes in the

logical structure of the data, while physical data independence insulates users from changes

in the physical storage of the data. We saw an example of logical data independence in the

answer to Exercise 1.2. Consider the Students relation from that example (and now assume

that it is not replaced by the two smaller relations). We could choose to store Students tuples

in a heap file, with a clustered index on the sname field. Alternatively, we could choose to

store it with an index on the gpa field, or to create indexes on both fields, or to store it as a

file sorted by gpa. These storage alternatives are not visible to users, except in terms of

improved performance, since they simply see a relation as a set of tuples. This is what is

meant by physical data independence.

答案 1.3 逻辑数据独立性意味着用户不受数据逻辑结构变化的影响，而物理数据独立

性意味着用户不受数据物理存储变化的影响。我们在练习 1.2 的答案中看到了一个逻

辑数据独立性的例子。考虑这个例子中的 Students 关系(现在假设它不会被两个较小

的关系取代)。我们可以选择在堆文件中存储 Students 元组，在 sname 字段中使用聚

集索引。或者，我们可以选择将其与 gpa 字段上的索引一起存储，或者在这两个字段

上创建索引，或者将其存储为按 gpa 排序的文件。这些存储替代方案对用户来说是不

可见的，除非在性能提升方面，因为他们只是把一个关系看作一组元组。这就是物理

数据独立性的含义。

Introduction to Database Systems

数据库系统导论

Exercise 1.4 Explain the di erence between external, internal, and conceptual sche-mas.ﬀ

How are these di erent schema layers related to the concepts of logical and physical dataﬀ

independence?

练习 1.4 解释外部、内部和概念模式之间的区别。这些不同的模式层是如何与逻辑和

物理数据独立的概念相关联的？

Answer 1.4 External schemas allows data access to be customized (and authorized) at the

level of individual users or groups of users. Conceptual (logical) schemas de-scribes all the

data that is actually stored in the database. While there are several views for a given

database, there is exactly one conceptual schema to all users. Internal (physical) schemas

summarize how the relations described in the conceptual schema are actually stored on disk

(or other physical media).

答案 1.4 外部模式允许在个人用户或用户组的层次上定制(和授权)数据访问。概念(逻

辑)模式描述了实际存储在数据库中的所有数据。虽然给定的数据库有几个视图，但

是对于所有用户来说只有一个概念模式。内部(物理)模式总结了概念模式中描述的关

系实际上是如何存储在磁盘(或其他物理媒体)上的。

External schemas provide logical data independence, while conceptual schemas o erﬀ

physical data independence.

外部模式提供逻辑数据独立性，而概念模式提供物理数据独立性。

Exercise 1.5 What are the responsibilities of a DBA? If we assume that the DBA is never

interested in running his or her own queries, does the DBA still need to understand query

optimization? Why?

练习 1.5 DBA 的职责是什么？如果我们假设 DBA 从来没有兴趣运行他或她自己的查

询，DBA 还需要理解查询优化吗？为什么？

Answer 1.5 The DBA is responsible for:

答案 1.5 DBA 负责:

Designing the logical and physical schemas, as well as widely-used portions of the

external schema.

设计逻辑和物理模式，以及广泛使用的外部模式部分。

Security and authorization.

安全和授权。

Data availability and recovery from failures.

数据可用性和故障恢复。

Database tuning: The DBA is responsible for evolving the database, in particular the

conceptual and physical schemas, to ensure adequate performance as user requirements

change.

数据库调优

: DBA

负责发展数据库，特别是概念和物理模式，以确保在用户需求

发生变化时具有足够的性能。

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