What are the principles for dividing hierarchical, networked and relational databases?

The principle of dividing hierarchical, network and relational databases is the connection between data. Hierarchical databases access data by record; network databases use network principles and methods to store data; relational databases store data in the form of rows and columns.

The principle of dividing hierarchical, network and relational databases is the connection between data.

The hierarchical database also accesses data by record. The most basic data relationship in the hierarchical data model is the basic hierarchical relationship, which represents a one-to-many relationship between two record types, also called parent-child relationship (PCR).

There is and is only one record type without parents in the database, which is called the root node. Other record types have one and only one parent. In the hierarchical model, the mapping from a node to its parents is unique, so for each record type (except the root node), you only need to point out its parents to express the overall structure of the hierarchical model. The hierarchical model is tree-like.

The most famous and typical hierarchical database system is IBM's IMS (Information Management System), which is the earliest large-scale database system program product developed by IBM.

Since its emergence in the late 1960s, it has now developed to IMSV6, providing support for advanced features such as clustering, N-way data sharing, and message queue sharing. This 30-year-old database product plays a new role in today's WWW application connections and business intelligence applications.

Network database is a database established based on network principles and methods and based on network data model. Generally refers to the network database system generated by the network database management system.

The network data model is a network structure with record types as nodes, that is, a node can have one or more subordinate nodes, or one or more superior nodes, two nodes There can even be multiple connections between them, such as the two record types of "teacher" and "course", and the two connections of "teaching" and "tutoring", which are called composite chains.

The value between two record types can be a many-to-many relationship. For example, a course is taken by multiple students, and a student takes multiple courses.

Relational database refers to a database that uses a relational model to organize data. It stores data in the form of rows and columns to facilitate user understanding. The series of rows and columns in a relational database are called Table, a group of tables makes up a database.

Users retrieve data in the database through queries, and a query is an execution code used to limit certain areas in the database. The relational model can be simply understood as a two-dimensional table model, and a relational database is a data organization composed of two-dimensional tables and the relationships between them.

Recommended tutorial: "MySQL Tutorial"

The above is the detailed content of What are the principles for dividing hierarchical, networked and relational databases?. For more information, please follow other related articles on the PHP Chinese website!