What needs to be modified to ensure the logical data independence of the database?

To ensure the independence of database logical data, what needs to be modified is: the image of the schema and the foreign schema. When the database schema changes, by adjusting the mapping relationship between external schemas/schemas, the application program does not have to be modified accordingly, thus ensuring the logical data independence between the data and the application program.

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

Data independence is one of the most basic characteristics of a 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 schemas that ensures that the data in the database system has high data independence. Data independence includes data logical independence and data physical independence.

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

The independence of data and program separates the definition of data from the program, and the DBMS is responsible for data access, thus simplifying the preparation of application programs and greatly reducing the maintenance and modification of application programs. .

Logical data independence

In order to realize the connection and conversion between the foreign schema and the schema of the database system, an image is established between the foreign schema and the schema, that is, the foreign schema/schema image. The external schema describing the local logical structure is linked to the schema describing the global logical structure through the mapping between the external schema and the schema. Since one schema corresponds to multiple foreign schemas, for each foreign schema, the database system has a foreign schema/schema image, which defines the corresponding relationship between the foreign schema and the schema. These image definitions are usually included in their respective In the description of the external mode

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