Entity-Relationship Diagram (ERD)
An ERD is a visual representation of the data model that represents the structure of a database. It is a powerful tool used in database design to illustrate the logical structure of a database in a graphical way. ERDs are particularly useful in understanding the relationships between different entities in a system.
ERD diagram concepts
Entities: Entities are objects or concepts that are represented in the database and are typically nouns. For example, in a university database, entities might include Student, Course, and Professor.
Attributes: Attributes are properties or characteristics that describe the entities. For example, a Student entity may have attributes like StudentID, Name, and DateOfBirth.
Relationships: Relationships depict how entities are related to each other. They establish connections between entities and can be one-to-one, one-to-many, or many-to-many. For instance, a Student entity might be related to a Course entity in a “takes” relationship.
Cardinality: Cardinality defines the numerical relationship between entities in a relationship. It indicates how many instances of one entity are related to another. Common cardinalities include one-to-one (1:1), one-to-many (1:N), and many-to-many (M:N).
Primary Key: A primary key is a unique identifier for a record within an entity. It helps ensure each record can be uniquely identified.
Foreign Key: A foreign key is a field in one table that refers to the primary key in another table. It establishes a link between the two tables.
Weak Entity: A weak entity is an entity that cannot be uniquely identified by its own attributes alone and relies on a related entity to provide the identification.
Identify Main Entities:
User Entities:
-Customer
-Administrator
-Seller
Product Entities:
-Product
-Category
-Brand
Order Entities:
-Order
-Order Item
Payment Entities:
-Payment
-Payment Method
Identify Attributes:
Customer Entity Attributes:
-CustomerID (Primary Key)
-Name
-Email
-Address
-Phone
Product Entity Attributes:
-ProductID (Primary Key)
-Name
-Price
-Description
-StockQuantity
Order Entity Attributes:
-OrderID (Primary Key)
-OrderDate
-TotalAmount
-Status (e.g., pending, shipped)
Payment Entity Attributes:
-PaymentID (Primary Key)
-Amount
-PaymentDate
-Status (e.g., successful, pending)
Define Relationships:
Customer-Order Relationship:
-One customer can place multiple orders (One-to-Many).
-Add a foreign key in the Order entity referring to CustomerID.
Order-Order Item Relationship:
-One order can have multiple order items, and each order item belongs to only one order (One-to-Many).
-Add a foreign key in the Order Item entity referring to OrderID.
Product-Order Item Relationship:
-One product can be included in multiple order items, and each order item is associated with one product (Many-to-One).
-Add a foreign key in the Order Item entity referring to ProductID.
Customer-Payment Relationship:
-One customer can make multiple payments (One-to-Many).
-Add a foreign key in the Payment entity referring to CustomerID.
Cardinality:
Customer-Order Cardinality:
-One customer can place many orders, but each order is placed by one customer.
Order-Order Item Cardinality:
-One order can have many order items, but each order item belongs to one order.
Product-Order Item Cardinality:
-One product can be in many order items, but each order item is associated with one product.
Customer-Payment Cardinality:
-One customer can make many payments, but each payment is made by one customer.
Final ERD
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