数据库如何处理数据库太大_网络数据库中的数据处理

数据库如何处理数据库太大

Before learning the data manipulation in a network model, we are discussing data manipulation language, so what is the data manipulation language?

在学习网络模型中的数据操作之前，我们正在讨论数据操作语言，那么什么是数据操作语言？

数据处理语言(DML) (Data Manipulation Language (DML))

A data manipulation language (DML) is used to perform tasks such as to search and retrieve, insert, delete, modify records from the database and to connect and disconnect records from the set occurrences.

数据操作语言(DML)用于执行任务，例如从数据库中搜索和检索，插入，删除，修改记录，以及将记录与所设置的事件连接和断开连接。

Host languages are a general-purpose programming language. The data manipulation language that is associated with the network model consists of record-at-a-time commands that are embedded in host languages. These embedded commands are also termed as data sublanguage in DML.

宿主语言是一种通用的编程语言。与网络模型关联的数据操作语言由嵌入在主机语言中的一次记录命令组成。这些嵌入式命令在DML中也称为数据子语言。

COBOL and PL/I are the most commonly used host languages. On the other hand, to show the program segments, PASCAL notation is augmented with network DML commands.

COBOL和PL / I是最常用的宿主语言。另一方面，为了显示程序段，使用网络DML命令来增强PASCAL表示法。

网络数据库操作 (Network Database Manipulation)

Basic Concepts for Network Database Manipulation...

网络数据库操作的基本概念...

In order to understand network data manipulation, we must get familiar with the basic concepts that show us, how data manipulation programs are written?

为了理解网络数据操纵 ，我们必须熟悉向我们展示的基本概念， 如何编写数据操纵程序？

There are two separate software systems, the database system, and the host programming language. Both the software systems are linked together by a common interface and only through this interface, they are allowed to communicate. It is important to identify specific records of the database as current records because DML commands are record-at-a-time.

有两种独立的软件系统，即数据库系统和主机编程语言。这两个软件系统都通过一个公共接口链接在一起，并且只有通过该接口才能进行通信。将数据库的特定记录标识为当前记录非常重要，因为DML命令是一次记录。

To keep track of the number of current records and set occurrences, DBMS uses the mechanism known as currency indicators. Also, to hold the records of different recode types, the host programming language requires local program variables, so that the host program can manipulate their contents. The set of these local variables in the program is termed as the User Work Area (UWA).

为了跟踪当前记录的数量并设置发生次数，DBMS使用称为货币指标的机制。同样，为了保存不同记录类型的记录，主机编程语言需要本地程序变量，以便主机程序可以操纵其内容。程序中这些局部变量的集合称为用户工作区(UWA)。

UWA is a set of program variables that are declared in the host program in order to communicate the contents of individual records between the DBMS and the host program. A program variable with the same format must be declared in the program, for each record type in the database schema.

UWA是在主机程序中声明的一组程序变量，以便在DBMS和主机程序之间传递各个记录的内容。对于数据库模式中的每种记录类型，必须在程序中声明具有相同格式的程序变量。

Currency Indicators

货币指标

In the network DML, to keep the trace of the search is critical as retrievals and updates are controlled by moving or navigating through the database records. Currency indicators keep the track of most recently accessed records and the set occurrences by DBMS. Each currency indicator can be termed as record pointer (or record address), that points to a single database record. Many currency indicators are used in network DBMS:

在网络DML中，保持跟踪是至关重要的，因为通过移动或浏览数据库记录来控制检索和更新。货币指示器跟踪最近访问的记录以及DBMS设置的事件。每个货币指标都可以称为记录指针(或记录地址)，它指向单个数据库记录。网络DBMS中使用了许多货币指标：

Current of record type:
当前记录类型：

DBMS keeps the track of most recently accessed record of each record type. The current record becomes undefined if no record gets accessed from that record type.
DBMS跟踪每种记录类型的最新访问记录。如果未从该记录类型访问任何记录，则当前记录将变为未定义。
Current of set type:
设定类型的电流：

DBMS keeps the track of most recently accessed set occurrence of each record type. Set which is the owner of the 16 member records, the set occurrence is stated by a single record from that set. Therefore the current set points to a record, although it is used to keep track of a set occurrence. The current set is undefined if the program has not accessed any record from that set type.
DBMS跟踪每种记录类型的最近访问集的发生情况。集合是16个成员记录的所有者，集合的出现由该集合中的单个记录表示。因此，当前集合指向记录，尽管它用于跟踪集合出现。如果程序尚未访问该集合类型的任何记录，则当前集合未定义。
Current of the run unit (CRU):
运行单元(CRU)的电流：

CRU is a database access program and gets executed on the computer system. In the database, CRU keeps track of the record most recently accessed by the program for each run unit such that this record can be from any record type.
CRU是数据库访问程序，可在计算机系统上执行。在数据库中，CRU跟踪程序最近为每个运行单元访问的记录，以便该记录可以来自任何记录类型。

Whenever a DML command get executed by a program, the currency indicators for record types and set types that are affected by the command get updated by DBMS.

每当程序执行DML命令时，DBMS都会更新该命令所影响的记录类型和集合类型的货币指标。

Status Indicators

状态指示灯

After each DML command gets executed, several status indicators return an indication of success or failure. With such indication, the program can check the values of these status indicators and take appropriate action, either to continue execution or to transfer to an error-handling routine.

在执行每个DML命令之后，几个状态指示器将返回成功或失败的指示。有了这样的指示，程序可以检查这些状态指示器的值并采取适当的措施，以继续执行或转移到错误处理例程。

Assuming DB_STATUS to be implicitly declared in the host program, we call the main status variable. The value of DB_STATUS indicates whether the command was successful or whether an exception occurred after each DML command is executed. The most common exception to occur in any DML command is the END_OF_SET (EOS) exception.

假设在主机程序中隐式声明了DB_STATUS ，我们将调用主状态变量。 DB_STATUS的值指示命令是否成功执行或在执行每个DML命令之后是否发生异常。在任何DML命令中最常见的异常是END_OF_SET(EOS)异常。