Database Type Overview

Database Type

Databases can be categorized into different types based on the data model. Currently, mature data models used in database systems include hierarchical models, network Zhuang models, and relational models. Next we will learn the following three models. Hierarchical Model The hierarchical model uses a tree structure to indicate the record type and Its Relationship. The basic features of the tree structure are: 1. There is only one node without a parent node; 2. Other nodes have a parent node. In a layered model, the node of the tree is a record type. The relationship between the previous record type and the next record type is 1: N. The layered model is like a inverted tree shown below. As follows: Note: You must specify an access path to search for records in a hierarchical database. This relational model does not support M: N connections. Mesh Model The links between nodes in the mesh model are not restricted by layers and can be connected at will. Therefore, her structure is the connected graph of nodes. The mesh model structure is characterized: 1. More than one node has no parent node; 2. At least one node has more than one parent node. The following is an example of a mesh model: Note: although the mesh model can reflect various complex relationships, the mesh model only supports 1: N connections for specific implementations. The M: N contact can be converted to 1: N contact. LINK model The essence of a relational model is to use several two dimensional tables to represent entities and their relationships. The link is defined by the Link name and attribute name. A link can be formally expressed: R (A1, A2, A3 ,..., AI ,...) Where: R is the link name, and AI is the link property name.