Database design specifications, the ER diagram, FIG model

(1) database design pros and cons:

• Bad database design:
  ① redundant data redundancy, waste of storage space.
  ② data updates and inserts an exception.
  ③ program poor performance.

• Good database design
  ① save storage space data.
  ② to ensure complete new data.
  ③ data to facilitate the development of application systems.

(2) the software development cycle, database design:

A complete project development need to go through:
1. Demand Analysis: Analyze the client's business and data processing needs.
2. Summary of design: ER model diagram design of the database, verify that the correct and complete information needs.
Detailed design: The three paradigms audit database structure, the ER model diagram converted to the database model diagram.
Coding: the physical implementation of the database, Coding applications.
After running the package design issue.

Database design steps:

• collect information
• Identify the entity (Entity)
• Identifying each entity attribute (Attribute) of
• The relationship between the identification entity (Relationship)

(3)E-R图(Entity Relationship Diagram)

ER diagram: the equivalent of drawing a database, and for communication between project members and other customers, to discuss whether the database design to meet customer demand.

Concept:

In addition to these three there is a straight line, a map showing the base contact sets:

Hotels database management system (ER diagram):

an entity - relationship diagram include: entities, attributes, contact.
(4) a database model of FIG.

FIG relationship ER step of converting mode:

• 1. Each entity relationship model is converted to R (U) in the form of
• 2. The establishment of inter-entity links conversion (1-1,1-n, nn)

Relational schema hotel management system database:

The system of inter-entity links are 1-n (to establish contact is the number of contacts for the entity's primary key 1 on the number of contacts for the entity-relationship model n's.):

Draw database model diagram step:

• New Database Model Diagram
• Add Entity
• Adding data columns and the corresponding properties
• Add the mapping relationships between entities

Original Address: https: //blog.csdn.net/weixin_43691058/article/details/93783658