Database principles and Technical Learning notes

The three stages of a database experience:

1, the artificial management stage:

Data managers: People

Data-oriented objects: an application

Data sharing: No sharing, great redundancy

Data independence: Not independent, completely dependent on the program

Structure of data: unstructured

Data Control capabilities: application control

2. File System phase: Features

Data Manager: File system

Data-oriented objects: an application

Data sharing: Poor sharing, high redundancy

Independence of data: poor independence

Structure of the data: there is structure in the record, the whole structure is unstructured

Data Control capabilities: application control

3. Database System phase: Features

Data Manager: Database management system

Data-oriented objects: the entire application system

Data sharing: high degree of sharing, low redundancy

Data independence: A high degree of physical independence and logical independence

Structuring of data: Holistic structuring with Data model description

Data control capabilities: Data security, integrity, concurrency control, and resiliency by a database management system

classification of two database models;

1 Hierarchy Model 2 mesh Model 3 Relationship model

Hierarchical model: There is only one root node, there are a number of leaf nodes, such as a group company, subordinate subsidiaries, subsidiaries under a number of departments, departments and employees, describes a one-to-many relationship

2. Mesh Data Model: Relationships between things are non-hierarchical, one node can have multiple parent nodes, and no parent nodes are allowed. For example Andy Lau, he is an actor, and he is a singer.

3. Relational Model: Represents a description of a relationship, a collection of properties for a class of things. For example, the relationship name (column 1, column 2, ...). Column N)

The main advantages and disadvantages of the hierarchical model:

The data itself is relatively simple, the system performance is better than the relational model and the network model, the disadvantage is that the insert and delete operations are more restrictive, the query child nodes must pass through the parent node.

The main advantages and disadvantages of the mesh data model:

The data structure is shallow, one node can inherit multiple parent nodes, the access efficiency is high, the structure is loose, and the complex structure is not conducive to unified management with the extension of application.

The main advantages and disadvantages of relational model: data structure is single, data operation is set operation.

Database principles and Technical Learning notes