E-R Graph is also called entity - Contact diagram (Entity Relationship Diagram), Provides a representation entity type , Methods of attributes and connections , A conceptual model used to describe the real world .
It is an effective method to describe the conceptual model of real world relations . Is a way to represent a conceptual relational model . use “ Rectangular box ” Represents a solid type , The name of the entity is indicated in the rectangle ; use “ Ellipse frame ” Or the rounded rectangle represents the properties of the entity , Combined use “ Solid line segment ” It is related to the “ Solid type ” Connect ;
use ” Diamond box “ Represents the cause of connection between solid types , Write the contact name in the diamond box , Combined use ” Solid line segment “ They are respectively connected with the entity type concerned , At the same time ” Solid line segment “ The type of connection on the sidebar
E-R The correctness of the graph design depends on whether the database designer can really grasp the business process of the application environment and the various objective objects involved in the business process and the activities among them , This requires accurate and in-depth analysis of user needs . These objects are recorded objectively if necessary , It's abstract E-R Entities in a graph （ Many related data describing entities are abstracted as attributes of entities , Many entities with the same attributes are abstracted into real bodies ）. If the activities between them need to be recorded , It's abstract E-R Connections in the diagram , This is E-R Key points of graphic design .