SQL Server Database learning Note-E-R model

The entity (entities) Contact (relationships) model abbreviation E-R model is also called the E-r method, which was first proposed by P.p.chen in 1976. There is also a key element of the Attributes-property, which provides a user-oriented expression method that is not constrained by any database management system (DBMS), and is widely used as a tool for data modeling in database design.

The E-r diagram, also known as entity-Contact graph (Entities Reationship Diagram), provides methods for representing entities, attributes, and relationships that describe the conceptual model of time to display (unlike the conceptual data model).

E-r Diagram Representation Method:

Entity: A rectangle indicating the name of the entity in the rectangle box. If it is a weak entity, a solid line rectangle is then set outside the rectangle.

Attribute (Attribute): is represented by an ellipse, and it is connected to the corresponding entity with a non-edge. If it is a multivalued attribute, then a solid ellipse is set outside the ellipse. If it is a derived property, it is represented by a dashed ellipse.

Contact (Relationship): With a diamond, the diamond box is indicated by the contact name, and the non-forward side is connected with the relevant entities, while in the non-edge side of the contact type (1:1, 1:n or m:n). In the case of a weak entity, the diamond is then set outside the diamond.

The relationship between conceptual data model and E-R model

The conceptual Data Model (conceptual) is also known as the information model. It is the abstraction of objective things and their connections, the modeling of the information world, the first abstraction of the real world to the information world, and a powerful tool for database designers to design the database. The E-R model is the most common method for the expression of conceptual models. Note: The E-R model is not completely equal to CDM.

The role of the E-r diagram:

Primarily used to communicate with customers, the goal is to have the programmer and the customer agree on this diagram.

SQL Server Database learning Note-E-R model