Theory and practice of database design < two > conceptual design and logic design

21. Conceptual Design

1.1 key knowledge of conceptual design

1.2 Discrimination

　　The difference between an entity and an attribute:

① entities can be further described by multiple attributes, but not attributes, which are non-subdivided/segmented atoms.

There is a connection between the ② entity or multiple entities, and the attribute is not.

　　The difference between an entity and a contact:

A ① connection cannot exist alone, and must be determined by the parties or partners it is associated with, and the entity is not required.

The code of the ② contact is determined by the main code of the entity it is associated with, and the code of the entity is independent of other entities or contacts.

　　In general, many people are apt to confuse ternary ties with three two-dollar links.

1.3 Attached image

Figure 1.1 Ternary linkage (relationship of three entities)

Figure 1.2 One-dollar link

Figure 1.3 Types of properties

Figure 1.4 Two RMB contact

Second, logical design

　　

"References"

Wu Yaihua. Database application System development process, technology and case study. Renmin University Press.

Theory and practice of database design < two > conceptual design and logic design