What is the abbreviation of E-R method?

#E-R method is the abbreviation of what method?

The E-R method is the abbreviation of "Entity-Relationship Approach".

It is an effective way to describe a conceptual model of real-world relationships. It is a way of representing a conceptual relationship model. Use "rectangular box" to represent the entity type, and write the entity name in the rectangular box; use "elliptical frame" or rounded rectangle to represent the attributes of the entity, and use "solid line segments" to connect it with the "entity type" of the corresponding relationship.

Use "diamond box" to indicate the cause of the connection between entity types, write the contact name in the diamond box, and use "solid line segments" to connect to the relevant entity types respectively, and mark next to "solid line segment" The type of contact (1:1, 1:n or m:n).

Composition elements:

The three basic elements that constitute the E-R diagram are entity type, attributes and relationships, and their representation method is:

1. Entity

It is generally believed that things that can be objectively distinguished from each other are entities. Entities can be specific people and things, or they can also be abstract concepts and connections. The key is that one entity can be distinguished from another entity, and entities with the same attributes have the same characteristics and properties. Use entity names and their attribute name sets to abstract and describe similar entities. In the E-R diagram, it is represented by a rectangle, and the entity name is written in the rectangular box; for example, student Zhang San and student Li Si are both entities. If it is a weak entity, put a solid rectangle outside the rectangle.

2. Attributes

A certain characteristic of an entity can be characterized by several attributes. Attributes cannot be separated from entities; attributes are relative to entities. It is represented by an ellipse in the E-R diagram, and undirected edges are used to connect it with the corresponding entities; for example, the student's name, student number, and gender are all attributes. If it is a multi-valued attribute, put a solid ellipse outside the ellipse. If it is a derived attribute, it is represented by a dotted ellipse.

3. Contact

Contact is also called relationship, which reflects the association within or between entities in the information world. The relationship within an entity usually refers to the relationship between the attributes that make up the entity; the relationship between entities usually refers to the relationship between different entity sets. It is represented by a diamond in the E-R diagram. The contact name is written in the diamond box, and undirected edges are used to connect it to the relevant entities. At the same time, the type of contact (1:1, 1:n or m:n) is marked next to the undirected edge. ). For example, there is a teaching relationship between teachers teaching students, and there is a course selection relationship when students choose courses. If it is a weak entity connection, put another rhombus outside the rhombus.

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