The data model reflects the relationship between the data of the thing itself and related things. The data model is used to describe data, organize data and operate data. It is a description of the characteristics of real-world data. The purpose of establishing a data model: Computers cannot directly process real things. Only by converting real things into digital data can computers recognize and process them.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Data Model (Data Model) is an abstraction of data characteristics. It is used to describe data, organize data and operate data. It is a description of real-world data characteristics.
The data model describes the static characteristics, dynamic behavior and constraints of the system from an abstract level, providing an abstract framework for the information representation and operation of the database system.
The purpose of establishing a data model: Computers cannot directly process real things. Therefore, only by converting real things into digital data can computers recognize and process them.
Components
The content described by the data model has three parts, namely data structure, data operations and data constraints.
①Data structure: The data structure in the data model mainly describes the type, content, nature of data and the relationship between data. Data structure is the basis of data model, and data operations and constraints are based on data structure. Different data structures have different operations and constraints.
②Data operations: Data operations in the data model mainly describe the operation types and operation methods on the corresponding data structure.
③Data constraints: Data constraints in the data model mainly describe the syntax and word meaning connections between data in the data structure, the constraints and dependencies between them, and the rules for dynamic changes in data to ensure the accuracy of the data. , valid and compatible
Level type
The data model is divided into three types according to different application levels: conceptual data model, logical data model, and physical data model.
Conceptual Data Model is a user-oriented and objective world-oriented model. It is mainly used to describe the conceptual structure of the world. It is used by database designers in designing In the initial stage, we get rid of the specific technical issues of computer systems and DBMS, and focus on analyzing data and the connections between data, etc., which has nothing to do with the specific data management system (Database Management System, DBMS for short). The conceptual data model must be replaced by a logical data model before it can be implemented in the DBMS.
Logical Data Model (Logical Data Model) is a model for database systems. It is a specific data model supported by DBMS, such as Network Data Model (Network Data Model) , hierarchical data model (Hierarchical Data Model) and so on. This model is both user-oriented and system-oriented, and is mainly used for the implementation of database management systems (DBMS).
The Physical Data Model (Physical Data Model) is a model oriented to the physical representation of computers. It describes the organizational structure of data on storage media. It is not only related to the specific DBMS, And it also depends on the operating system and hardware. Each logical data model has its corresponding physical data model when implemented. In order to ensure its independence and portability, DBMS implements most of the physical data model automatically by the system, while designers only design special structures such as indexes and aggregations.
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