箭头所指实体集表示映射的“1”方,线段对应的实体集表示映射的“多”一方 one-to-one one-to-many。一名教师可以指导多名学生 many-to-many 全参与用双线 另一种表达: 一名学生只能被一位教师指导,一位教师可以指导多名学生 Ternary Relationship自学 弱实体:没有主键的实体。弱实体集依赖于一个实际存在的确定的...
#3) Many to One Relationships Many entities from an entity set are related to one entity in another entity set. For example, many students belong to the same class. #4) Many-to-Many Relationships Many entities from an entity set are related to many entities in another entity set. For ex...
ERD, 即 entity Relationship diagram, 实体关系图。使用一组定义的符号,如矩形、菱形、椭圆和连接线来描述实体、关系及其属性的相互联系。 ER图的组成部分 ER 图由实体、关系和属性组成。 并且不同的记法有不同的符号。 这里介绍比较常用的两种技法:Chen notation style和Crow's Foot style Chen notation style P...
Notes: If true, the N-ary Association represents the many-to-many recursive relationship. For one-to-many and one-to-one recursive relationships, we suggest using the normal Relationship connector. Sometimes you might want to limit the stretch of the diamond-shape Relationship connectors; ...
Entity Relationship Diagram Symbols — Crow’s Foot notationSymbol Meaning Relationships (Cardinality and Modality) Zero or One One or More One and only One Zero or More Many - to - One a one through many notation on one side of a relationship and a one and only one on the other a ...
Foreign keys are created any time an attribute relates to another entity in a one-to-one or one-to-many relationship. Each car can only be financed by one bank, therefore the primary key BankId from the Bank table is used as the foreign key FinancedBy in the Car table. This BankID ...
Anentity relationship diagramshowing the entities of a simple order processing system. ERD notations Here are the notations supported by ERD: Entity, database view, sequence, one-to-one relationship, one-to-many relationship, many-to-many relationship,stored procedure,stored procedureresultset,trigger...
3. Relationship A relationship is represented by diamond shape in ER diagram, it shows the relationship among entities. There are four types of relationships: 1. One to One 2. One to Many 3. Many to One 4. Many to Many 1. One to One Relationship ...
entity relationship diagram 英 [ˈentəti rɪˈleɪʃnʃɪp ˈdaɪəɡræm] 美 [ˈentəti rɪˈleɪʃnʃɪp ˈdaɪəɡræm]网络 ...
One to many: (1 : n) (or many to one). For example, a class with multiple students Here FK (FOREIGN KEY), represents a foreign key. Foreign keys are not necessarily primary keys, but must be unique indexes. A foreign key represents a related connection between two relationships. A tab...