EER diagram (EERD)
An EER diagram (Enhanced Entity-Relationship Diagram) is a visual representation of the data model that represents the relationships between entities in a database system
An EER diagram (Enhanced Entity-Relationship Diagram) is a visual representation of the data model that represents the relationships between entities in a database system. It is an extension of the traditional Entity-Relationship (ER) model, enhancing it with additional features.
The EER diagram offers more expressiveness and allows the representation of complex concepts and relationships, making it more suitable for designing complex databases. It adds new concepts such as subclasses, inheritance, and relationships with attributes.
In an EER diagram, there are several key elements:
1. Entities: Entities represent real-world objects or concepts that are stored in the database. Each entity is represented by a rectangle in the diagram, with its name written inside.
2. Attributes: Attributes describe the properties or characteristics of an entity. They are represented by ovals connected to the entity rectangle. Attributes can be simple (with a single value) or composite (with multiple values).
3. Relationships: Relationships depict the associations between two or more entities. They are represented by diamonds connecting related entities. Relationships can have cardinality indicators to show the number of occurrences allowed. For example, a “one-to-many” relationship between a student and a course indicates that a student can enroll in multiple courses, but a course can have only one instructor.
4. Inheritance: EER diagrams support inheritance, allowing the creation of subclasses that inherit attributes and relationships from a parent class. Subclasses are represented by rectangles with dashed or solid lines connecting them to their parent classes.
5. Multivalued attributes: EER diagrams support multivalued attributes, which are attributes that can have multiple values. They are represented by double ovals connected to the entity.
6. Weak entities: Weak entities are entities that depend on another entity to exist. They are represented by a double rectangle in the diagram.
Overall, EER diagrams provide a comprehensive and conceptual representation of the database structure, allowing designers to model complex relationships and constraints. They are an essential tool in database design, helping to organize and visualize the database schema before implementing it in a database management system.
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