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  • 数据库系统概念第六版习题答案(完整英文版)。看书过程会进行翻译,笔记。
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  • 数据库系统概念第六版课后答案,较为详细,有步骤解释。
  • Practice Exercises 1.1 This chapter has described several major advantages of a database system. What are two disadvantages? Answer: Two disadvantages associated with database systems are listed below...
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  • ~包括用户、应用系统、应用开发工具、操作系统数据库等等 Major disadvantages of file system Data redundancy and inconsistency Difficulty in accessing data Data isolation (multiple files and ...

    Database concepts

    Database-management system (DBMS)

    A collection of interrelated data and a set of programs to access those data

    Database-system applications

       

    File-process systems

    The typical file-processing system is supported by a conventional operating system

    The system stores permanent records in various files, and it needs different application programs to extract records from, and add records to, the appropriate files

        Data inconsistency

        (*drawback of file system)

    The various copies of the same data may no longer agree

    ~比如一个学生选了双学位,那么在两个学位下面都要存储他的信息,造成冗余

    ~而且,如果学生的地址改变了,那么可能一处进行了修改,一处没有,造成不一致

        Consistency constraints

        (*drawback of file system)

    When new constraints are added, it is difficult to change the program to enforce them

     

    Data abstraction

    The need for efficiency has led designers to use complex data structures to represent data in the database

    Since users are stupid, developers hide the complexity from users through several levels of abstraction:c

    Physical level: how the data are actually stored

    Logical level: what data are stored in the database

    View level: users only need part of the database, so we need to simplify their interaction with the system

    Instance

    The collection of information stored in the database at a particular moment

    实例,类比于某个时刻某个变量的值

    Schema

    The overall design of the database

    模式,类比于变量的声明

        physical schema

    The database design at the physical level

        logical schema

    The database design at the logical level

    Physical data independence

    Although implementation of the simple structure at logical level may involve complex physical-level structures, the user of the logical level does not need to be aware of that

    Data models

    Underlying the structure of a database is the data model: a collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints

    A data model provides a way to describe the design of a database at the physical, logical and view levels

        entity-relationship model

    (chpt 7)

    E-R data model uses a collection of basic objects, called entities, and relationships among these objects

    An entity is a "thing" or "object" in the real world

        relational data model

    (chpt 2-6)

    The relation model uses a collection of tables to represent both data and the relationships among those data

    Tables are also known as relations

        object-based data model

    Extending the E-R model with notions of  encapsulation, methods (functions), and object identity

        semistructured data model

    Permits the specification of data where individual data items of the same type may have different sets of attributes

    Database languages

    SQL is a database language

        data-defining language(DDL)

    To specify the database schema by a set of definitions

    Also used to specify additional properties of the data

        data-manipulation language(DML)

    A language that enables users to access or manipulate data as organized by the appropriate  data model

        query language

     

    Metadata

    元数据是“数据的数据”,用于描述数据的特征或性质以及该数据的内容,是数据库的一部分

    ~例如(数据名称、定义、长度)或者(数据来源、存储位置、拥有者)

    Application program

    A program that is used to interact with the database

    Normalization

    To generate a set of relation schema that allows us to retrieve information without unnecessary redundancy, yet also allows us to retrieve information easily

    Data dictionary

    DDL gets some input and returns output

    The output of DDL is called data dictionary, which contains metadata - that is, data about data

    The data dictionary is considered to be a special type of table that can only be access and update by the database system itself (not a regular user)

    Storage manager

    Provides the interface between the low-level data stored in the database and the application system and queries submitted to the system

    Including: authorization and integrity manager; transaction manager; file manager; buffer manager

    Query processor

    The query processor components include:

    DDL interpreter: interprets DDL statements

    DML compiler: translate DML statements into a low-level construction that engine understands

    Query evaluation engine: executes low-level instructions generated by the DML compiler

    Transactions

    事务

    A transaction is a collection of operations that performs a single logical function in a database application

        atomicity

    All-or-none: Fund transferred or not at all

        failure recovery

    Detect system failures and restore the database to the state that existed prior to the occurrence of the failure

        concurrency control

    The consistency of data may no longer be preserved even though the individual transaction is correct

    Concurrency-control system is to control the interaction among the concurrent transactions

    Two- and three-tier database architectures

    2-tier: the application resides at the client machine

    3-tier: the client machine acts as merely a front end and does not contain any direct database calls

    Instead, the client communicates with an application server through a forms interface; then  the application server in turn communicates with the database system

    3-tier is more suitable for large applications, and those applications running on the web

    Data mining

    Semiautomatically analyzing larger database to find useful patterns

    Database administrator (DBA)

    A person who has the central control of both the data and the programs that access those data

     

     

    Data

    The data describe one particular enterprise

    数据是可以记录和存储在计算机介质上的关于对象和事件的事实

    Or 数据是在用户环境中具有意义和重要性的对象和事件的存储表示

    Information

    人能看懂的数据

    Metadata

    元数据是“数据的数据”,用于描述数据的特征或性质以及该数据的内容,是数据库的一部分

    ~例如(数据名称、定义、长度)或者(数据来源、存储位置、拥有者)

    Database

    Database is the collection of data, usually contains information relevant to an enterprise

    长期存储在计算机内,有组织的,可共享的大量数据集合

    Database-management system (DBMS)

    互相关联的数据集合(database)和一组用于访问这些数据的程序

    目标:提供一种方便、高效地存储数据库信息的途径

    Database system (DBS)

    在计算机系统中引入数据库后的系统构成

    ~包括用户、应用系统、应用开发工具、操作系统、数据库等等

    Major disadvantages of file system

    Data redundancy and inconsistency

    Difficulty in accessing data

    Data isolation (multiple files and formats)

    Integrity problem (integrity constraints)

    Atomicity of updates

    Concurrent access by multiple users

    Security problems (hard to provide some instead of all data)

    Database schema

    数据库模式,也被称为数据库内涵,是指对数据库的描述

    是在设计过程中规定的,不会经常改变

    Database instance

    某一时刻数据库中的数据,也被称为数据库的外延or数据库的状态

    数据库的实例会经常变化

    Relation schema

    The database schema describes how the tables (relations) connect and are built, while a relation schema is essentially the schema for a table

    Relation instance

     

    Data abstraction (3-layer architecture)

    对应书上第七页,实质上是data abstraction的三个层次

     

        physical level (internal schema)

    内模式、内层、物理层。表示数据库的物理存储结构,和数据存储的路径及细节。

        logical level (conceptual schema)

    概念模式、中间层、概念层。用于为用户描述数据库的结构,注重实体、数据类型、用户操作和约束,并且隐藏了存储的细节。

    使用表示型数据模型(E-R模型)来描述概念模式

    使用实现型数据模型(OO模型)来进行概念模式设计

        view level (external schema)

    外模式、外层、视图层。描绘了用户感兴趣的部分数据库,隐藏其他部分。

    使用表示型数据模型(E-R模型)加以实现

     

    三层模式的主要目的是保证数据的独立性,即对底层的修改不会对高层造成影响。

        physical data independence

    物理数据独立性:概念模式不会受内模式变化的影响。

        logical data independence

    逻辑数据独立性:外模式不会受概念模式变化的影响。(x独立:x变化但上一层不受影响)

    Database languages

     

        procedural languages

    Procedural DMLs require a user to specify what data are needed and how to get those data

        declarative languages

    Declarative DMLs (non-procedural DMLs) require a user to specify what data are needed without specifying how to get those data

    SQL:

     

        DDL

    a data-definition language (DDL) to specify the database schema

        DML

    a data-manipulation language (DML) to express database queries and updates

    What DML can do: Retrieval, Insertion, Deletion, Modification

        Query language (Select)

    DML能做的是增删改(取),query能做的是(查),但是可以混为一谈

    query是请求查询的语句,query language是DML中的取数据操作

    A query is a statement requesting the retrieval if the information

    A query language is the portion of DML that involves information retrieval

    Types of DBS users

    Database users:

    4 types differentiated by the way they expect to interact with the system:

    Naïve users: too young too naïve, use interfaces

    Application programmers: they use rapid application development tools to program

    Sophisticated users: interact with the system without writing programs, but they use database query languages to form their request ~an analyst

    Specialized users: write specialized database systems

    Database administrators

    Functions of DBAs

    Schema definition

    Storage structure and access-method definition

    Schema and physical-organization modification

    Granting of authorization for data access

    Routine maintenance

    DBMS architectures

    ACID of transactions and meaning

    Atomicity: either all operations of the transaction are reflected properly in the database, or none are

    Consistency: execution of a transaction in isolation (no other concurrent transaction) preserves the consistency of the database

    Isolation: though Ti and Tj execute concurrently, it appears to Ti that either Tj has not begun or has finished

    That is, each transaction is unaware of other transactions executing concurrently

    Durability: after a transaction completes successfully, the changes it has made to the database persist, even if there are system failures

    展开全文
  • 东北大学数据库系统概念期末复习与个人笔记(笔记参考自数据库系统概念(原书第六版)与课程教学PPT)
  • 数据库系统概念 第六版 习题答案 英文版

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