oracle中dbms

1)实例 (1) Instances)

What is the Instance? If we look towards it in real life, we refer instance as an occurrence of something at a particular moment of time. In Database Management system, there are a lot of changes occurring over time to the information rapidly within the moments as the data get inserted, manipulated and deleted in parallel. The collection of information stored in the database at a particular moment is called an instance of the database.

什么是实例？ 如果我们在现实生活中着眼于此，我们将实例称为在特定时间某个事件的发生。 在数据库管理系统中，随着数据的并行插入，操作和删除，信息随时间的变化会Swift发生很多变化。 在特定时刻存储在数据库中的信息集合称为数据库实例 。

2)模式 (2) Schemas)

What is Schema? In the database management system, the overall design of the database is called the database schema. Schema gets changed rarely, and if so, changes altogether. A database schema corresponds to the variable declarations together with associated type definitions in a program.

什么是架构？ 在数据库管理系统中，数据库的总体设计称为数据库架构 。 模式很少更改，如果更改，则完全更改。 数据库模式与程序中的变量声明以及关联的类型定义相对应。

At any given instant, each variable has a particular value and the values of the variables in a program at a point in time correspond to an instance of a database schema.

在任何给定的时刻，每个变量都有一个特定的值，并且程序中某个时间点的变量值对应于数据库模式的实例 。

To understand the concept of database schemas and instances, we can do it through the analogy to a program written in a programming language.

为了理解数据库模式和实例的概念，我们可以通过类似于用编程语言编写的程序来实现。

数据库模式的类型 (Types of databse schemas)

There are several schemas in a Database system that is partitioned depending on the levels of abstraction:

数据库系统中有几种模式，这些模式根据抽象级别进行分区：

1. Physical Schema

   物理架构

   The

   的

   physical schema describes the database design at the physical level.

   物理模式描述了物理级别的数据库设计。

2. Logical Schema

   逻辑架构

   The

   的

   logical schema describes the database design at the logical level.

   逻辑模式在逻辑级别描述数据库设计。

Image source: https://sites.google.com/site/pnusicte11/_/rsrc/1472872626548/lesson-2/Screen%20Shot%202016-01-21%20at%207.52.51%20AM.png

图片来源：https://sites.google.com/site/pnusicte11/_/rsrc/1472872626548/lesson-2/Screen%20Shot%202016-01-21%20at%207.52.51%20AM.png

The physical schema is hidden beneath the logical schema, and it can be changed easily without affecting the application programs.

物理模式隐藏在逻辑模式下，可以轻松更改而不影响应用程序。

If the application programs are not dependent on the physical schema then they are said to display physical data independence, and so if the physical schema got to change in any case then, the application programs are needed to be rewritten.

如果应用程序不依赖于物理模式，则称它们显示物理数据独立性，因此，如果物理模式在任何情况下都必须更改，则需要重写应用程序。

Including these, in a database, there are several schemas present at the view level and called subschemas that describe different views of the database.

包括这些在内，在数据库中，在视图级别存在几种模式，这些模式描述了数据库的不同视图。

By far, the logical schema is the most important among all schemas due to its tremendous effect on application programs, as the programmers construct applications by using the logical schema.

到目前为止，由于逻辑方案对应用程序的巨大影响，因此逻辑方案是所有方案中最重要的，因为程序员使用逻辑方案构造应用程序。

翻译自: https://www.includehelp.com/dbms/instances-and-schemas-in-dbms.aspx

oracle中dbms