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This article mainly introduces how to ensure the logical data independence of the database, the article is very detailed, has a certain reference value, interested friends must read it!

To ensure the independence of the database logical data, what needs to be modified is the image of the schema and the external schema. When the database schema changes, the mapping relationship between the external schema / schema is adjusted so that the application does not have to be modified accordingly, thus ensuring the logical data independence between the data and the application.

To ensure the independence of the database logical data, what needs to be modified is the image of the schema and the external schema.

The independence of data is one of the most basic features of database system. Data independence means that applications and data structures are independent of each other and do not affect each other. In the three-tier schema architecture, data independence refers to the ability of the database system to change the schema at a certain level without changing the schema at the upper level. It is the two-layer image between the three-level modes that ensures the high data independence of the data in the database system. Data independence includes data logical independence and data physical independence.

Data independence is also one of the most important goals of database system. It makes the data independent of the application.

The independence of the data and the program separates the definition of the data from the program, and DBMS is responsible for the access of the data, which simplifies the compilation of the application program and greatly reduces the maintenance and modification of the application program.

Logical data independence

In order to realize the connection and transformation between the external schema and the schema of the database system, an image is established between the external schema and the schema, namely the external schema / schema image. Through the mapping between the external schema and the schema, the external schema describing the local logical structure is connected with the schema describing the global logical structure. Because a schema corresponds to multiple external schemas, for each external schema, the database system has an external schema / schema image that defines the correspondence between the external schema and the schema. These image definitions are usually included in the description of the respective external schema.

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