属性(Attribute):实体所具有的特征,用椭圆形表示,并通过无向边与实体相连 学生这个实体的多个属性 属性分为唯一属性( unique attribute)和非唯一属性,唯一属性指的是唯一可用来标识该实体实例或者成员的属性,用下划线表示,一般来讲实体都至少有一个唯一属性。 ER图的关系(relationship)用来表现数据对象与数据对象之间的...
An entity can be place, person, object, event or a concept, which stores data in the database. The characteristics of entities are must have an attribute, and a unique key. Every entity is made up of some ‘attributes’ which represent that entity. Examples of entities: Person:Employee, ...
数据库设计(二):ER图绘制 上一节我们提到ER图由3中基本的要素(属性/字段(Attribute)、关系(Relation)、实体(Entity))组成,那么在这一节中我们介绍不同在ER图中如何去表示这些要素。 属性/字段...属性和名属性组合而成。 属性在ER图中的表示方法: 关系(Relation) 在上节我们提到,关系有3中性质:度(Degree)...
An article that contains everything on ER diagrams, entity symbols, attribute symbols, relationship symbols, cardinality, and several other ER diagram notations used worldwide.
The ER diagram example below shows an entity with some attributes in it. Primary Key Also known as PK, a primary key is a special kind of entity attribute thatuniquely defines a record in a database table. In other words, there must not be two (or more) records that share the same ...
ERD stands for entity relationship diagram. People also call these types of diagrams ER diagrams and Entity Relationship Models. An ERD visualizes the relationships between entities like people, things, or concepts in a database. An ERD will also often visualize the attributes of these entities. ...
Aweakentity does not have a key attribute that uniquely identifies each instance of that entity. Instead, it is identified by the combination of apartial keyon the weak entity itself and the key of another entity, which it is related to via anidentifying relationship. A weak entity must have...
Attribute names are recorded in the rectangle representing an entity under entity name. For instance, an entity "human being" may have such attributes as gender, year of birth, first name, etc.It is the specialized Entity Relationship diagram symbols, and the meanings of those symbolsEntity ...
2. Attribute 3. Relationship 1. Entity An entity is an object or component of data. An entity is represented as rectangle in an ER diagram. For example: In the following ER diagram we have two entities Student and College and these two entities have many to one relationship as many studen...
Which entities make up your database? Represent each one with a rectangle, and space them apart from each other so you have room to add attributes and relationships to your diagram in the next steps. Add Attributes to Each Entity Each entity should have at least one attribute – a group ...