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This article mainly introduces the logical data independence in the database is provided by what image, has a certain reference value, friends in need can refer to. I hope you will learn a lot after reading this article. Next, let the editor take you to learn about it.

Logical data independence is provided by the "external schema / schema" image. When the schema changes, the database administrator can make corresponding changes to the images of each external schema / schema, which can keep the external schema unchanged. The application program is written according to the external mode of the data, so that the application program does not need to be modified, which ensures the logical independence of the data and the program, referred to as the logical independence of the data.

The three-level schema structure of the database system means that the database system is composed of external schema, schema and internal schema.

External schema, also known as subpattern or user pattern, is the description of the logical structure and characteristics of local data that database users (including application programmers and end users) can see and use, and it is the data view of database users. it is a logical representation of data related to an application.

Schema, also known as logical schema and conceptual schema, is the description of the logical structure and characteristics of all data in the database, and is the common data view of all users. It is the middle layer of database schema structure, which not only does not involve the physical storage details and hardware environment of data, but also has nothing to do with specific applications, development tools and languages.

Internal schema, also known as storage mode, is the description of the physical structure and storage mode of data, and the representation of data in the database.

The database management system provides the following two-layer images between the three-level modes to ensure that the data in the database system has high logical independence and physical independence.

External schema / schema image: when the schema changes, the database administrator makes corresponding changes to the images of each external schema / schema, which can keep the external schema unchanged. The application program is written according to the external mode of the data, so that the application program does not need to be modified, which ensures the logical independence of the data and the program, referred to as the logical independence of the data.

The independence of logical data indicates the degree of independence of an application when the schema changes. Today's systems can provide logical data independence in the following aspects:

(1) add new record types to the mode, as long as the relationship between the original record types is not destroyed.

(2) add new connections between the original record types.

(3) add new data items to some record types.

Schema / internal schema image: when the storage structure of the database changes, the database administrator can make corresponding changes to the schema / internal schema image, which can keep the schema unchanged, so that the application does not have to change. It ensures the physical independence of data and programs, which is referred to as data physical independence.

Thank you for reading this article carefully. I hope it is helpful for everyone to share what image provides the content of logical data independence in the database. At the same time, I also hope that you can support it, pay attention to the industry information channel, and find out if you encounter problems. Detailed solutions are waiting for you to learn!

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