数据库系统概念第六版引言习题

Posted 2020-06-27

1  数据库的两个不足之处

A  数据库系统的建立需要更多的知识，技能，金钱，时间。

B 数据库系统的复杂性可能产生不好的影响。

 

2 列出JAVA或C++之类的语言中的类型说明系统和数据库系统使用的数据定义语言的5个不同之处（暂时不懂）

a. Executing an action in the DDL results in the creation of an object in
the database; in contrast, a programming language type declaration
is simply an abstraction used in the program.

b. Database DDLs allows consistency constraints to be specified, which
programming language type systems generally do not allow. These
include domain constraints and referential integrity constraints.

c. Database DDLs support authorization, giving different access rights to
different users. Programming language type systems do not provide
such protection (at best, they protect attributes in a class from being
accessed by methods in another class).

d. Programming language type systems are usually much richer than
the SQL type system. Most databases support only basic types such
as different types of numbers and strings, although some databases
do support some complex types such as arrays, and objects.

e. A database DDL is focussed on specifying types of attributes of relations;
in contrast, a programming language allows objects, and collections
of objects to be created.

 

3 列出为一个企业建立数据库的六大步骤

A  定义企业的高层次的需求(这一步生成
一个文档被称为系统需求规范。)

B 定义一个包含所有适当的类型的数据模型和数据的关系。

C 定义数据的完整性约束。

D 定义物理层。

E •对于每一个要解决的问题,定期(如。、任务
是由职员或Web用户)定义一个用户界面
执行任务,编写必要的应用程序
实现用户界面。 

F 建立数据库

 

4  列出大学需要维护的三种不同信息

图书馆书籍信息

学校教职工信息

学校经费信息

 

5 假设你要建立一个类似于 YOUTUBE的视频节点。考虑如果数据保存在文件系统的各个缺点，讨论每一个缺点与存储实际的视频数据和关于视频的元数据

 

Data redundancy and inconsistency. This would be relevant to metadata
to some extent, although not to the actual video data, which is not
updated. There are very few relationships here, and none of them can
lead to redundancy.
• Difficulty in accessing data. If video data is only accessed through
a few predefined interfaces, as is done in video sharing sites today,

this will not be a problem. However, if an organization needs to find
video data based on specific search conditions (beyond simple keyword
queries) if meta data were stored in files it would be hard to find
relevant data without writing application programs. Using a database
would be important for the task of finding data.
• Data isolation. Since data is not usually updated, but instead newly
created, data isolation is not a major issue. Even the task of keeping
track of who has viewed what videos is (conceptually) append only,
again making isolation not a major issue. However, if authorization is
added, there may be some issues of concurrent updates to authorization
information.
• Integrity problems. It seems unlikely there are significant integrity
constraints in this application, except for primary keys. if the data is
distributed, there may be issues in enforcing primary key constraints.
Integrity problems are probably not a major issue.
• Atomicity problems. When a video is uploaded, metadata about the
video and the video should be added atomically, otherwise therewould
be an inconsistency in the data. An underlying recovery mechanism
would be required to ensure atomicity in the event of failures.
• Concurrent-access anomalies. Since data is not updated, concurrent
access anomalies would be unlikely to occur.
• Security problems. These would be a issue if the system supported
authorization.

1.6 在WEB查找中使用的关键字查询和数据库查询很不一样 请列出这两者之间 在查询表达方式和查询结果是什么方面的主要差异

 

查询中使用的Web通过提供的列表来指定关键词

没有特定的语法。结果通常是一个有序的列表url,见到的片段信息的内容的url。在相反,数据库查询有一个特定的语法允许复杂的查询指定。在关系世界总是一个查询的结果表。

 

1.7 列出四个你使用过的很可能使用了数据库来存储持久数据的应用   

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