oracle中dbms

1)實例 (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.

什么是實例？ 如果我們在現實生活中著眼于此，我們將實例稱為在特定時間某個事件的發生。 在數據庫管理系統中，隨著數據的并行插入，操作和刪除，信息隨時間的變化會Swift發生很多變化。 在特定時刻存儲在數據庫中的信息集合稱為數據庫實例 。

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.

什么是架構？ 在數據庫管理系統中，數據庫的總體設計稱為數據庫架構 。 模式很少更改，如果更改，則完全更改。 數據庫模式與程序中的變量聲明以及關聯的類型定義相對應。

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.

在任何給定的時刻，每個變量都有一個特定的值，并且程序中某個時間點的變量值對應于數據庫模式的實例 。

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

為了理解數據庫模式和實例的概念，我們可以通過類似于用編程語言編寫的程序來實現。

數據庫模式的類型 (Types of databse schemas)

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

數據庫系統中有幾種模式，這些模式根據抽象級別進行分區：

Physical Schema

物理架構

The

的

physical schema describes the database design at the physical level.

物理模式描述了物理級別的數據庫設計。

Logical Schema

邏輯架構

The

的

logical schema describes the database design at the logical level.

邏輯模式在邏輯級別描述數據庫設計。

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

圖片來源：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.

物理模式隱藏在邏輯模式下，可以輕松更改而不影響應用程序。

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.

如果應用程序不依賴于物理模式，則稱它們顯示物理數據獨立性，因此，如果物理模式在任何情況下都必須更改，則需要重寫應用程序。

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

包括這些在內，在數據庫中，在視圖級別存在幾種模式，這些模式描述了數據庫的不同視圖。

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.

到目前為止，由于邏輯方案對應用程序的巨大影響，因此邏輯方案是所有方案中最重要的，因為程序員使用邏輯方案構造應用程序。

翻譯自: https://www.includehelp.com/dbms/instances-and-schemas-in-dbms.aspx

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