数据库系统架构

Database management system is partitioned into modules for different functions. Some functions may be provided by the operating system. Broadly the functional component of the database system are:

数据库管理系统分为不同功能的模块。 某些功能可能由操作系统提供。 数据库系统的功能组件大致包括：

数据库管理系统的组成 (Components of database management system)

1)查询处理器 (1) Query Processor)

It is one of the functional components of DBMS. The database manager understands that the query processor translates statements into low-level instructions in a query language. It may also attempt to find an equivalent but more efficient form.

它是DBMS的功能组件之一。 数据库管理器了解查询处理器将语句翻译成查询语言的低级指令。 它还可能尝试找到等效但更有效的形式。

It contains the following components:

它包含以下组件：

1. DML Compiler

   DML编译器

   The DML compiler converts DDL(data definition language) statements in the form of tables which stored metadata in a data dictionary. It also performs query optimization.

   DML编译器以表的形式转换DDL(数据定义语言)语句，该表将元数据存储在数据字典中。 它还执行查询优化。

2. DDL Interpreter

   DDL解释器

   It is a device which interprets the DDL statements and some records into the data dictionary.

   它是一种将DDL语句和一些记录解释为数据字典的设备。

3. Query Evaluation Engine

   查询评估引擎

   It executes low-level instructions generated by DML(data manipulation language) compiler. They mainly deal with solving all problems related to queries and query processing. It helps database system simplify and facilitate access to data.

   它执行由DML(数据操作语言)编译器生成的低级指令。 它们主要处理与查询和查询处理有关的所有问题。 它有助于数据库系统简化并促进对数据的访问。

2)存储管理器(数据库管理器) (2) Storage Manager (Database Manager))

The database manager is the part of database management which manages all the organizations, storage and updating of data and provides an interface between the low-level data and some programs. The storage manager is responsible for many tasks. It provides interaction with the file manager.

数据库管理器是数据库管理的一部分，它管理所有组织，数据的存储和更新，并提供低级数据和某些程序之间的接口。 存储管理器负责许多任务。 它提供与文件管理器的交互。

The important components include:

重要组件包括：

1. File Manager

   文件管理器

   It manages the allocation of disk space and data structures used to represents information on the disk.

   它管理磁盘空间的分配以及用于表示磁盘信息的数据结构。

2. Database Manager

   数据库管理员

   It is the interface between low-level data and applications programs and queries.

   它是低级数据与应用程序和查询之间的接口。

3. Transaction Manager

   交易经理

   Transaction manager ensures that the database remains in a consistent(correct) state despite system failures. Examples- power failure and operating system crashes.

   事务管理器可确保即使系统出现故障，数据库仍保持一致(正确)状态。 示例-电源故障和操作系统崩溃。

4. DML Pre-compiler

   DML预编译器

   DML pre-complier converts DDL statements which are embedded in an application program into a normal procedure calls. The pre-compiler interacts with the query processor.

   DML预编译器将嵌入在应用程序中的DDL语句转换为常规过程调用。 预编译器与查询处理器进行交互。

5. DML Compiler

   DML编译器

   It converts DDL statements to a set of tables containing metadata stored in a data directory.

   它将DDL语句转换为一组表，这些表包含存储在数据目录中的元数据。

DBMS的三级体系结构 (3 level Architecture of DBMS)

A DBMS is a buffer between the applications programs and end users and some of the database which is designed to fulfill the features of data independence. In 1975 the American national standards institute standards planning and requirement committee (ANSI-SPARC) proposed three-level architecture identified three levels of abstraction.

DBMS是应用程序和最终用户以及某些旨在实现数据独立性功能的数据库之间的缓冲区。 1975年，美国国家标准协会标准计划和要求委员会(ANSI-SPARC)提出了三级体系结构，该体系结构确定了三级抽象。

These three levels are sometimes to schemas or views:

这三个级别有时涉及架构或视图：

1. The external or user level

   外部或用户级别

   This level describes the user’s or applications programmer’s view of the database. The same view can be shared by some programs or users.

   此级别描述了用户或应用程序程序员对数据库的视图。 某些程序或用户可以共享同一视图。

2. The conceptual level

   概念层面

   The conceptual level describes the view of all the data in the database. The relationships between the data and the constraints applicable to the database. This level describes a logical view of the database means a view locking implementations details.

   概念级别描述了数据库中所有数据的视图。 数据与适用于数据库的约束之间的关系。 此级别描述了数据库的逻辑视图，该视图表示锁定实现的详细信息。

3. The internal or physical level

   内部或身体层面

   This level describes the way by which the data stored in the memory and the approach by which the may be accessed. This level describes a physical view of the database

   此级别描述了存储在存储器中的数据的方式以及访问数据的方式。 此级别描述了数据库的物理视图

Each level is described in terms of schema i.e. a map of the database. The three-level architecture is designed in such a way that it implements data independence through two levels of mapping that between the external schema and the conceptual schema and that between the conceptual schema and the physical schema.

每个级别都根据架构(即数据库的映射)进行描述。 三级体系结构的设计方式是，它通过两个层次的映射来实现数据独立性，这两个层次的映射分别是外部模式和概念模式之间以及概念模式和物理模式之间的映射。

References:

参考文献：

• https://www.slideshare.net/piyushlucky/23246406-dbmsunit1

  https://www.slideshare.net/piyushlucky/23246406-dbmsunit1

• https://www.relationaldbdesign.com/relational-database-design/module3/three-schema-architecture.php

  https://www.relationaldbdesign.com/relational-database-design/module3/three-schema-architecture.php

• http://www.cs.sfu.ca/CourseCentral/354/zaiane/material/notes/Chapter1/node21.html

  http://www.cs.sfu.ca/CourseCentral/354/zaiane/material/notes/Chapter1/node21.html

翻译自: https://www.includehelp.com/dbms/architecture-of-database-management-system.aspx

数据库系统架构