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联系,例如学生的实体和成绩表的实体之间有一定的联系,每个学生都有自己的成绩表,这就是一种关系,...
ER Diagramstands for Entity Relationship Diagram, also known as ERD is a diagram that displays the relationship of entity sets stored in a database. In other words, ER diagrams help to explain the logical structure of databases. ER diagrams are created based on three basic concepts: entities, ...
在数据库设计中，ER图（Entity-Relationship Diagram）是不可或缺的工具，它以直观的图形方式展示了实体(entity)、属性(attribute)和关系(relationship)三要素。让我们一起探索它们的结构和应用场景。1. ER图的三大元素实体(entity)，作为数据模型中的核心单元，每个实体都有独特的标识，如学生实体"张三"和...
Siu Road, Shatinage = 55phone = 1234-5667employee 1name = Cheung Tinaddress = 25, Big Street, Shatinage = 20phone = 2338-7779employee 2COMP2318ER DiagramThe ER model can be presented graphically by an ER diagramageEmployeenameaddressphoneentityattributeCOMP2319Different attribute typesSimple a ...
Label your components: Include text labels to provide additional information, such as entity names, attribute names, data types, and constraints. You can also number each component and reference them in a separate legend for clarity. Define relationships: Use lines or connectors to illustrate relatio...
ER图由三大要素构成:实体(Entity)、属性(Attribute)和关系(Relationship)。实体代表了现实世界中的一些对象、事物或概念;属性描述了实体的特征或属性,每个实体可以拥有多个属性,如姓名、年龄、性别等;关系则表达了实体间的连接或联系,可以是一对一、一对多或多对多的关系。
Multi-value:More than one attribute value is denoted, such as multiple phone numbers for a person. Single-value:Just one attribute value. The types can be combined, such as: simple single-value attributes or composite multi-value attributes. ...
In any database, there are two types of data we observe, 1. Object or Entity and 2. Attribute. An object can be anything, any real-world entity, and the attribute data are the properties of the object that describes the entity. The diagram that represents various objects with their attr...
An attribute can also have their own attributes. These attributes are known asCompositeattributes. ER Diagram: Relationship A Relationship describes relation betweenentities. Relationship is represented using diamonds or rhombus. There are three types of relationship that exist between Entities. ...
2.1 ER- Diagram Notations Rectangles: This symbol represent entity types Ellipses : Symbol represent attributes Diamonds: This symbol represents relationship types Lines: It links attributes to entity types and entity types with other relationship types ...