Shulou(Shulou.com)06/01 Report--

What this article shares with you is about what needs to be modified to ensure the data independence of the database. The editor thinks it is very practical, so I share it with you. I hope you can learn something after reading this article. Let's take a look at it with the editor.

In order to ensure the data independence of the database, what needs to be modified is the mapping relationship between 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 independence between the data and the application.

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.

Logically, a database structure can be divided into three layers: external schema, internal schema and conceptual schema. To improve data independence in the database system, DBMS provides two-tier images between these three-level schemas. As the basic characteristics of the database system, the independence of data and programs depends on these three-level patterns and two-level images.

Conceptual schema, also known as schema, is a description of the global logical structure of the database, which is constructed by the database designer to synthesize all user data and according to a certain point of view.

In the three-level schema of the database system, the conceptual schema is in the middle tier, and there is only one conceptual schema in a database, which does not involve the physical storage details of the data and the hardware environment, but also has nothing to do with the specific application program and programming language.

The external schema is also called the subschema, which is the interface between the user and the database, and is the description of the logical structure and characteristics of the local data that the database user can see and use.

Internal schema, also known as storage mode, is the description of the physical structure and storage mode of the data in the database, and the representation of the data in the database. A database has only one internal schema. The internal schema is the lowest level of DBMS management, and it is the physical abstraction of data stored on the physical storage device.

The ability to modify a schema definition at a certain level without affecting the schema above it is called data independence. There are two levels of data independence: physical independence and logical independence.

The above is what needs to be modified to ensure the data independence of the database. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.