1.2 Data Model

1. Meaning: Used in databases to abstract, represent and process data and information in the real world

2. Classification: Conceptual models, physical models, and logical models

Among them, the logical model includes: Hierarchical model, net model, relational model

The constituent elements of the data model:

1. Data structure: A description of the static characteristics of the system

2. Data manipulation: A description of the dynamic characteristics of the data

3. Integrity constraints: Entity integrity, referential integrity, user-defined integrity

Second, conceptual model--representation method: E-r diagram

Will draw a e-r chart

Third, the commonly used data model

1. Classification

1. Non-relational model: hierarchical model; NET model

2. Relational model

3. Object-oriented model

4. Object Relational Model

2. Basic Hierarchy Model

It means records and a one-to-many relationship between them (no many-to-many relationships)

3. Hierarchical model

There is only one node and there are no parent nodes (root node).

Nodes other than root have and have only one parent node

4. Mesh structure

Allow more than one node to have two parents;

A node can have more than one parent.

5. Relational model

1) Data structure

2) Manipulation: Set operation, that is, the operation of the whole table (different from the non-relational model: record operation)

3) integrity constraint: Entity ..., reference ..., user-defined

4) Storage structure: A table used to represent the storage between entities and entities;

5) Advantages and disadvantages: Based on the concept of mathematics, the concept of a single, the storage path to the user is transparent, so that on the one hand to ensure the independence of the data, on the other hand, it caused the query request to be optimized

1.2 Data Model