ER diagram, also known as entity-relationship diagram (Entity Relationship Diagram), provides a method of representing entity types, attributes and connections, and is used to describe the real world.
conceptual model
.
method
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The ER method is short for Entity-Relationship Approach. It is an efficient way to describe the structural model of real-world concepts. It is a way to represent the conceptual model. The entity type is represented by a rectangle, and the entity name is written in the rectangular frame; the attribute of the entity is represented by an ellipse, and an undirected edge is used to connect it with the corresponding entity type; the diamond is used to represent the entity type. connection between the
The name of the connection is written in the diamond
box, and the undirected edge is used to connect with the relevant entity type, and the type of connection (1:1, 1:n or m:n) is marked next to the undirected edge.
Element
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There are four components in the ER diagram as follows:
E-R
Rectangular box: Indicates the entity, and the entity name is recorded in the box.
Diamond
box: Indicates contact, enter the contact name in the box.
Oval Box: Indicates the attribute of the entity or relationship, enter the attribute name in the box. for
The main attribute
name, underscore its name.
Connection: between entities and attributes; between entities and connections; connections and attributes are connected with a straight line, and the type of connection is marked on the straight line. (For a one-to-one relationship, write 1 in the direction of the connection between the two entities; for a one-to-many relationship, write 1 on the one side and N on the many side; for a many-to-many relationship, write 1 on the two Write N and M in the direction of entity connection.)[1]