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One way to depict the connections between various database elements is with an Entity Relationship Diagram, which is sometimes called an ER diagram. An ER Diagram is an essential tool in DBMS when creating the database. In modern companies, an Entity Relationship Diagram serves as a preview of all the user requirements. The database administrators receive it later for database design.
What is an Entity Relationship Diagram?
The ER Diagram is a graphical representation of the relationship between entities that will be recorded in a database. A database’s structural design is essentially what the ER Diagram is. The objective of this framework is to define the relationship between the entities in the database using specialised symbols. The three main components of an Entity Relationship Diagram are entities, characteristics, and relationships.
The accompanying figure shows the relationship between the two entities, Student and Course. The course-student interaction is termed many-to-many because multiple students can choose the same course, and a single student can choose multiple courses. Attributes held by the student entity include Stu_Id, Stu_Name, and Stu_Age. Course entities have properties like Cou_ID and Cou_Name.
In database management systems, what is the purpose of using ER diagrams?
The following are some of the benefits of using an Entity Relationship Diagram:
• It aids in conceptualising the database and determining which fields should be embedded for each entity.
• It provides a clearer picture of the data that will be stored in the database.
• It simplifies things and lets database designers build databases faster.
• It provides a way to describe elements using Entity-Relationship models.
• It provides a sneak peek at the database’s internal structure, which is helpful for users
Symbols Used in ER Diagrams
• Rectangles: One way to represent entity types in an Entity Relationship Diagram is with this symbol.
• Ellipse: This shape stands for characteristics
• Diamonds: This stone stands for different kinds of relationships.
• Lines: It connects entity types to other relationship types and attributes to entity types.
• Primary key: The attributes are highlighted in the primary key.
• Double Ellipses: Double ellipses stand for attributes with multiple values.
Components of Entity Relationship Diagram
Entity
An entity can consist of both living and non-living parts.
As an Entity Relationship Diagram, it displays an entity as a rectangle.
Take a student study course as an example; in this setup, the student and the course are considered separate entities.
Weak Entity
A “weak entity” is dependent on another.
In the ER diagram, you can see the entity that isn’t as strong as a double rectangle.
With its primary key attribute, the school number, the entity “school” in the following example is robust. Because it lacks a primary key and serves primarily as a discriminator, the classroom could be a stronger entity in comparison to the school.
Attribute
An entity’s attributes are a representation of its characteristics.
An oval shape can be used to represent an attribute in an Entity Relationship Diagram.
Key Attribute
Each entity in an entity collection has a unique identifier or critical attribute.
A crucial attribute’s text is highlighted.
Take a student entity as an example; the roll number can be used to distinguish one student from another.
Composite Attribute
A composite attribute consists of numerous other qualities.
An oval shows a composite attribute, and other ovals are related to the composite attribute oval.
Multivalued Attribute
Multivalued qualities can hold more than one value.
The double oval form is employed to symbolise an attribute with several values.
Derived Attribute
A derived attribute can be constructed from other entity attributes.
The ER diagram shows the derived attribute as the dashed oval.
Relationship
In the ER diagram, the diamond shape represents a relationship.
It shows the connection between two things.
The student and the class are both things in the following example, and study is the connection between them.
One-to-One Relationship
A one-to-one relationship exists when there is a connection between two entities wherein one entity’s element is linked to another’s element.
An example would be the fact that each student is only issued a single identification card.
One-to-Many Relationship
A one-to-many relationship exists when one entity’s element is linked to multiple entities’ elements.
For example, while a single client can place an order, many customers cannot place the same order.
Many-to-One Relationship
Two entities with multiple connected elements have a many-to-one connection.
Many students may be registered in a course, but they can only choose one.
Many-to-Many Relationship
A “many-to-many” relationship exists when two entities have more than one element, each linked to the other.
For instance, a person can work on multiple projects, and each project can employ many people.
Conclusion
It is common practice to illustrate database architecture with an Entity Relationship Diagram in DBMS. The ability to see the database’s structure before implementing it is helpful for users and database developers.
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