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What is ER diagram?
What is an ERD diagram?
What is an Entity Relationship Diagram (ERD)?
Can ER diagrams be used in other contexts?
What is an entity relationship diagram?
What is relationship type in ER diagram?
An entity relationship diagram (ER diagram or ERD) is a visual representation of how items in a database relate to each other. ERDs are a specialized type of flowchart that conveys the relationship types between different entities within a system.
- Why Use Er Diagrams in DBMS?
- Symbols Used in Er Model
- What Is Entity?
- What Is Entity Set?
- What Is Attributes?
- Types of Attributes
- Relationship Type and Relationship Set
- Degree of A Relationship Set
- What Is cardinality?
- Participation Constraint
ER diagrams represent the E-R model in a database, making them easy to convert into relations (tables).ER diagrams provide the purpose of real-world modeling of objects which makes them intently useful.ER diagrams require no technical knowledge and no hardware support.These diagrams are very easy to understand and easy to create even for a naive user.ER Model is used to model the logical view of the system from a data perspective which consists of these symbols: 1. Rectangles: Rectangles represent Entities in the ER Model. 2. Ellipses: Ellipses represent Attributes in the ER Model. 3. Diamond: Diamonds represent Relationships among Entities. 4. Lines: Lines represent attributes to entities and ...
An Entity may be an object with a physical existence – a particular person, car, house, or employee – or it may be an object with a conceptual existence – a company, a job, or a university course.
An Entity is an object of Entity Type and a set of all entities is called an entity set. For Example, E1 is an entity having Entity Type Student and the set of all students is called Entity Set. In ER diagram, Entity Type is represented as: We can represent the entity set in ER Diagram but can’t represent entity in ER Diagram because entity is row ...
Attributes are the properties that define the entity type. For example, Roll_No, Name, DOB, Age, Address, and Mobile_No are the attributes that define entity type Student. In ER diagram, the attribute is represented by an oval.
1. Key Attribute
The attribute which uniquely identifies each entity in the entity set is called the key attribute. For example, Roll_No will be unique for each student. In ER diagram, the key attribute is represented by an oval with underlying lines.
2. Composite Attribute
An attribute composed of many other attributes is called a composite attribute. For example, the Address attribute of the student Entity type consists of Street, City, State, and Country. In ER diagram, the composite attribute is represented by an oval comprising of ovals.
3. Multivalued Attribute
An attribute consisting of more than one value for a given entity. For example, Phone_No (can be more than one for a given student). In ER diagram, a multivalued attribute is represented by a double oval.
A Relationship Type represents the association between entity types. For example, ‘Enrolled in’ is a relationship type that exists between entity type Student and Course. In ER diagram, the relationship type is represented by a diamond and connecting the entities with lines. A set of relationships of the same type is known as a relationship set. Th...
The number of different entity sets participating in a relationship set is called the degree of a relationship set. 1. Unary Relationship: When there is only ONE entity set participating in a relation, the relationship is called a unary relationship. For example, one person is married to only one person. 2. Binary Relationship: When there are TWO e...
The number of times an entity of an entity set participates in a relationship set is known as cardinality . Cardinality can be of different types: 1. One-to-One: When each entity in each entity set can take part only once in the relationship, the cardinality is one-to-one. Let us assume that a male can marry one female and a female can marry one ma...
Participation Constraint is applied to the entity participating in the relationship set. 1. Total Participation – Each entity in the entity set must participate in the relationship. If each student must enroll in a course, the participation of students will be total. Total participation is shown by a double line in the ER diagram. 2. Partial Partic...
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Dec 21, 2023 · What is an Entity Relationship Diagram (ERD)? An Entity Relationship Diagram (ERD) is a type of diagram that lets you see how different entities (e.g. people, customers, or other objects) relate to each other in an application or a database.
What is an Entity Relationship Diagram (ERD)? See ultimate guide to ER diagrams including a video overview, origins, uses, examples, components, limitations, and guidelines on how to draw them for free in Lucidchart.
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 entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects, places, concepts or events in an information technology (IT) system.
Mar 23, 2024 · What is an ER diagram? An Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and how they relate to each other. It is a tool used to design and model relational databases, and shows the logical structure of the database.
