Data mode of database system

Data model is the representation of information model in the data world. Data models can be divided into three categories: hierarchical model, network model and relational model.

(1) hierarchical model

Hierarchical model is a data model that describes entities and their relationships in a tree structure. In this structure, each record type is represented by a node, and the relationship between record types is represented by directed line segments between nodes. Each parent node can have multiple child nodes, but each child node can only have one parent node. This structure determines that the hierarchical database system organized by hierarchical model can only handle one-to-many entity relationships.

(2) Grid model

Grid model allows a node to have multiple parents and children at the same time. Therefore, compared with the hierarchical model, the network structure is more universal and can directly describe the entities in the real world. It can also be considered that hierarchical model is a special case of grid model.

(3) Relational model Relational model is a data model that uses a two-dimensional table structure to represent entity types and relationships between entities. Its basic assumption is that all data are represented by mathematical relations.