ER diagram
FIG entity also called ER - FIG contact, provides a way to represent entity types, attributes and links, is typical of an ER diagram in FIG.
FIG ER consists of four main components:
1 entity
Entities are all kinds of things that exist in the objective world, or an abstract event, we can call it an entity. On the one hand, the entity can be a real-world entity curriculum, teachers entity, student entity, individual workers. All in all, an entity may be a subset of the set of reality, it can be all kinds of abstract objects. Entity by rectangles shown in FIG ER.
2 Properties
Properties can be considered an entity in the feature, the entity is described by attributes, such as student entities school, name, sex and other attributes.
Properties ER diagram to represent an ellipse.
3 Contact
Contact includes two aspects, one is the link between the entities and attributes, such as the link between the driver and the driver of the above figure number; on the other hand is the link between the entity and the entity, the entity between students and courses ties.
Contact a diamond in the ER diagram to represent.
Such contact can be divided into three kinds
1-one contact (referred to as 1: 1)
2-many link (1: n)
Contact 3-many (m: n)
usefulness
ER is typically used in FIG conceptual data model.