An Diagram (ERD) is a visual representation of the relationships between entities in a database. Entities are objects or concepts that have s. An Attribute is a characteristic of an entity that describes some aspect of it. Relationships define how entities are connected to each other. specifies the number of instances of one entity that can be associated with the number of instances of another entity.
In a , multiple instances of one entity can be related to multiple instances of another entity. To represent this type of relationship, an or is used. This table includes the keys of the entities involved in the relationship, acting as a bridge between them. is a unique identifier for each record in a table, while is a field that identifies a record in another table.
There are three levels of ERD: Conceptual, Logical, and Physical. A focuses on the high-level view of the relationships between entities. A adds details like data types and constraints. A includes specifics such as indexes and physical storage. Each level helps in understanding and designing the database structure effectively.
