What is the definition of Entity-Relationship Model in database?
The Entity-Relationship (ER) Model is a conceptual framework used in database design to represent and organize data. It provides a way to visually depict the relationships between different entities within a system. Here are the key components of the ER model:
Entities: These are objects or things in the real world that have a distinct existence. An entity can be a physical object (like a car or a person) or a concept (like a course or a project). Each entity is represented by a rectangle in an ER diagram.
Attributes: These are the properties or characteristics of an entity. For example, a "Person" entity might have attributes such as Name, Age, and Address. Attributes are typically represented by ovals connected to their respective entities.
Relationships: These define how entities are related to one another. For example, a "Student" entity might be related to a "Course" entity through an "Enrolled In" relationship. Relationships are represented by diamonds in an ER diagram.
Cardinality: This specifies the number of instances of one entity that can or must be associated with each instance of another entity. Common cardinalities include one-to-one, one-to-many, and many-to-many.
Keys: These are attributes that uniquely identify an entity within an entity set. A primary key is a specific attribute or a combination of attributes that uniquely identifies each entity instance.
The ER model is often used as a preliminary step in database design, allowing designers to create a visual representation of the data requirements and relationships before implementing the actual database schema. ER diagrams are a common tool for this purpose, providing a clear and structured way to communicate the design to stakeholders.